[compilers] Use a pre-configure setup step

[Steelskin]

• Add a preliminary step to export the context for the compiler
  configuration step. This makes it easier to debug the compiler
  configuration step by seeing the full command line invocation on the
  GHA page.

[Steelskin]

PTAL. This is how the compilers configure step shows up as before this change:

$CxxFlags = "/GS- /Gw /Gy /Oi /Oy /Z7 /Zc:inline /Zc:preprocessor /Zc:__cplusplus /D_DISABLE_CONSTEXPR_MUTEX_CONSTRUCTOR"
  $SwiftFlags = ""
  $EXTRA_FLAGS = @()
  
  if ( "Windows" -eq "Windows" ) {
    $SWIFTC = cygpath -m (Get-Command swiftc).Source
    # Use toolchain clang to avoid broken __prefetch intrinsic on arm64 in Clang 18.
    # TODO: Use llvm-19 when available. See https://github.com/compnerd/swift-build/issues/846
    $CLANG_LOCATION = Split-Path (Get-Command swiftc).Source
    if ( "amd64" -eq "arm64" ) {
      $EXTRA_FLAGS += "-D CMAKE_SYSTEM_PROCESSOR=AMD64".Split()
      $EXTRA_FLAGS += @("-D", "CMAKE_SYSTEM_NAME=Windows")
      $CACHE="C:\a\swift-build\swift-build/SourceCache/swift/cmake/caches/Windows-aarch64.cmake"
  
      # FIXME(compnerd) re-enable runtimes after we sort out compiler-rt
      (Get-Content C:\a\swift-build\swift-build/SourceCache/swift/cmake/caches/Windows-aarch64.cmake).Replace(' runtimes', '') | Set-Content C:\a\swift-build\swift-build/SourceCache/swift/cmake/caches/Windows-aarch64.cmake
    } else {
      $CACHE="C:\a\swift-build\swift-build/SourceCache/swift/cmake/caches/Windows-x86_64.cmake"
    }
    $CC = "cl"
    $CXX = "cl"
  
    # Workaround for compiler and STL version mismatch on Windows.
    $CxxFlags += " -D_ALLOW_COMPILER_AND_STL_VERSION_MISMATCH"
    $SwiftFlags += " -Xcc -D_ALLOW_COMPILER_AND_STL_VERSION_MISMATCH"
  
    $SDKROOT = cygpath -m ${env:SDKROOT}
    $CLANG_LOCATION = cygpath -m $CLANG_LOCATION
    $LIBPYTHON_PATH = "${env:PYTHON_LOCATION_amd64}/libs/python[3](https://github.com/thebrowsercompany/swift-build/actions/runs/12587696230/job/35084714847#step:23:3)9.lib"
    $PYTHON_INCLUDE_DIR = "${env:PYTHON_LOCATION_amd6[4](https://github.com/thebrowsercompany/swift-build/actions/runs/12587696230/job/35084714847#step:23:4)}/include"
    $PYTHON_BINARY="python.exe"
    $ExeSuffix = ".exe"
    Remove-Item env:\SDKROOT
  } elseif ( "Windows" -eq "Darwin" ) {
    # Default swiftc comes from /usr/bin and is not compatible with the toolchain.
    $CLANG_LOCATION = "${env:HOME}/Library/Developer/Toolchains/swift-6.0.1-RELEASE.xctoolchain/usr/bin"
    $SWIFTC = Join-Path $CLANG_LOCATION "swiftc"
  
    # We need to use llvm-17 to build the compiler on macOS. We get it from the Swift toolchain.
    $CC = Join-Path $CLANG_LOCATION "clang"
    $CXX = Join-Path $CLANG_LOCATION "clang++"
    $CACHE = "C:\a\swift-build\swift-build/SourceCache/swift/cmake/caches/Darwin-amd64.cmake"
    $SDKROOT = xcrun --sdk macosx --show-sdk-path
    $EXTRA_FLAGS += "-D CMAKE_SYSTEM_PROCESSOR=AMD64".Split()
    $EXTRA_FLAGS += @("-D", "CMAKE_SYSTEM_NAME=Darwin")
    # TODO: Use early-swift-driver on Windows too.
    $EXTRA_FLAGS += @("-D", "SWIFT_EARLY_SWIFT_DRIVER_BUILD=C:\a\swift-build\swift-build/BinaryCache/swift-driver/bin")
    $LIBPYTHON_PATH = "${env:pythonLocation}/lib/python3.9/config-3.9-darwin/libpython3.9.a"
    $PYTHON_INCLUDE_DIR = "${env:pythonLocation}/include/python3.9"
    $PYTHON_BINARY="python3"
    $ExeSuffix = ""
  }
  
  $SwiftFlags += " -sdk `"${SDKROOT}`""
  
  cmake -B C:\a\swift-build\swift-build/BinaryCache/1 `
        -C "${CACHE}" `
        -D CMAKE_BUILD_TYPE=Release `
        -D CMAKE_C_COMPILER="${CC}" `
        -D CMAKE_C_COMPILER_LAUNCHER=sccache `
        -D CMAKE_C_FLAGS="/GS- /Gw /Gy /Oi /Oy /Z7 /Zc:inline /Zc:preprocessor" `
        -D CMAKE_CXX_COMPILER="${CXX}" `
        -D CMAKE_CXX_COMPILER_LAUNCHER=sccache `
        -D CMAKE_CXX_FLAGS="${CxxFlags}" `
        -D CMAKE_Swift_COMPILER="${SWIFTC}" `
        -D CMAKE_Swift_COMPILER_WORKS=YES `
        -D CMAKE_Swift_FLAGS="${SwiftFlags}" `
        -D CMAKE_EXE_LINKER_FLAGS="-incremental:no -debug -opt:ref -opt:icf" -D CMAKE_SHARED_LINKER_FLAGS="-incremental:no -debug -opt:ref -opt:icf" `
        -D CMAKE_FIND_PACKAGE_PREFER_CONFIG=YES `
        -D CMAKE_INSTALL_PREFIX=C:\a\swift-build\swift-build/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain/usr `
        @EXTRA_FLAGS `
        -G Ninja `
        -S C:\a\swift-build\swift-build/SourceCache/llvm-project/llvm `
        -D CLANG_TABLEGEN="C:\a\swift-build\swift-build/BinaryCache/0/bin/clang-tblgen${ExeSuffix}" `
        -D CLANG_TIDY_CONFUSABLE_CHARS_GEN="C:\a\swift-build\swift-build/BinaryCache/0/bin/clang-tidy-confusable-chars-gen${ExeSuffix}" `
        -D LLDB_TABLEGEN="C:\a\swift-build\swift-build/BinaryCache/0/bin/lldb-tblgen${ExeSuffix}" `
        -D LLVM_CONFIG_PATH="C:\a\swift-build\swift-build/BinaryCache/0/bin/llvm-config${ExeSuffix}" `
        -D LLVM_EXTERNAL_SWIFT_SOURCE_DIR=C:\a\swift-build\swift-build/SourceCache/swift `
        -D LLVM_NATIVE_TOOL_DIR=C:\a\swift-build\swift-build/BinaryCache/0/bin `
        -D LLVM_TABLEGEN="C:\a\swift-build\swift-build/BinaryCache/0/bin/llvm-tblgen${ExeSuffix}" `
        -D LLVM_USE_HOST_TOOLS=NO `
        -D SWIFT_BUILD_DYNAMIC_SDK_OVERLAY=NO `
        -D SWIFT_BUILD_DYNAMIC_STDLIB=NO `
        -D SWIFT_BUILD_REMOTE_MIRROR=NO `
        -D SWIFT_BUILD_SWIFT_SYNTAX=YES `
        -D SWIFT_CLANG_LOCATION=${CLANG_LOCATION} `
        -D SWIFT_ENABLE_EXPERIMENTAL_CONCURRENCY=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_CXX_INTEROP=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_DISTRIBUTED=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_DIFFERENTIABLE_PROGRAMMING=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_OBSERVATION=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_STRING_PROCESSING=YES `
        -D SWIFT_ENABLE_SYNCHRONIZATION=YES `
        -D SWIFT_NATIVE_SWIFT_TOOLS_PATH=C:\a\swift-build\swift-build/BinaryCache/0/bin `
        -D SWIFT_PATH_TO_LIBDISPATCH_SOURCE=C:\a\swift-build\swift-build/SourceCache/swift-corelibs-libdispatch `
        -D SWIFT_PATH_TO_SWIFT_SYNTAX_SOURCE=C:\a\swift-build\swift-build/SourceCache/swift-syntax `
        -D SWIFT_PATH_TO_STRING_PROCESSING_SOURCE=C:\a\swift-build\swift-build/SourceCache/swift-experimental-string-processing `
        -D SWIFT_PATH_TO_SWIFT_SDK="${SDKROOT}" `
        -D CLANG_VENDOR=compnerd.org `
        -D CLANG_VENDOR_UTI=org.compnerd.dt `
        -D cmark-gfm_DIR=C:\a\swift-build\swift-build/BinaryCache/Library/cmark-gfm-0.29.0.gfm.13/usr/lib/cmake `
        -D LibXml2_DIR=C:\a\swift-build\swift-build/BinaryCache/Library/libxml2-2.11.5/usr/lib/cmake/libxml2-2.11.5 `
        -D PACKAGE_VENDOR=compnerd.org `
        -D SWIFT_VENDOR=compnerd.org `
        -D LLVM_PARALLEL_LINK_JOBS=8 `
        -D SWIFT_PARALLEL_LINK_JOBS=8 `
        -D LLVM_APPEND_VC_REV=NO `
        -D LLVM_VERSION_SUFFIX="" `
        -D LLDB_PYTHON_EXE_RELATIVE_PATH=${PYTHON_BINARY} `
        -D LLDB_PYTHON_EXT_SUFFIX=.pyd `
        -D LLDB_PYTHON_RELATIVE_PATH=lib/site-packages `
        -D Python3_EXECUTABLE=C:\hostedtoolcache\windows\Python\3.9.10\x64\python.exe `
        -D Python3_INCLUDE_DIR=$PYTHON_INCLUDE_DIR `
        -D Python3_LIBRARY=$LIBPYTHON_PATH `
        -D Python3_ROOT_DIR=$env:pythonLocation

And after:

if ( "Windows" -eq "Windows" ) {
    $ExeSuffix = ".exe"
    Remove-Item env:\SDKROOT
  } elseif ( "Windows" -eq "Darwin" ) {
    $ExeSuffix = ""
  }
  
  cmake -B C:\a\swift-build\swift-build/BinaryCache/1 `
        -C "C:\a\swift-build\swift-build/SourceCache/swift/cmake/caches/Windows-x86_64.cmake" `
        -D CMAKE_BUILD_TYPE=Release `
        -D CMAKE_C_COMPILER="cl" `
        -D CMAKE_C_COMPILER_LAUNCHER=sccache `
        -D CMAKE_C_FLAGS="/GS- /Gw /Gy /Oi /Oy /Zc:inline /Zc:preprocessor" `
        -D CMAKE_CXX_COMPILER="cl" `
        -D CMAKE_CXX_COMPILER_LAUNCHER=sccache `
        -D CMAKE_CXX_FLAGS="/GS- /Gw /Gy /Oi /Oy /Zc:inline /Zc:preprocessor /Zc:__cplusplus /D_DISABLE_CONSTEXPR_MUTEX_CONSTRUCTOR -D_ALLOW_COMPILER_AND_STL_VERSION_MISMATCH" `
        -D CMAKE_Swift_COMPILER="C:/Users/runneradmin/AppData/Local/Programs/Swift/Toolchains/6.0.0+Asserts/usr/bin/swiftc.exe" `
        -D CMAKE_Swift_COMPILER_WORKS=YES `
        -D CMAKE_Swift_FLAGS=" -Xcc -D_ALLOW_COMPILER_AND_STL_VERSION_MISMATCH -sdk "C:/Users/runneradmin/AppData/Local/Programs/Swift/Platforms/6.0.0/Windows.platform/Developer/SDKs/Windows.sdk/"" `
        -D CMAKE_EXE_LINKER_FLAGS="" -D CMAKE_SHARED_LINKER_FLAGS="" `
        -D CMAKE_FIND_PACKAGE_PREFER_CONFIG=YES `
        -D CMAKE_INSTALL_PREFIX=C:\a\swift-build\swift-build/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain/usr `
         `
        -G Ninja `
        -S C:\a\swift-build\swift-build/SourceCache/llvm-project/llvm `
        -D CLANG_TABLEGEN="C:\a\swift-build\swift-build/BinaryCache/0/bin/clang-tblgen${ExeSuffix}" `
        -D CLANG_TIDY_CONFUSABLE_CHARS_GEN="C:\a\swift-build\swift-build/BinaryCache/0/bin/clang-tidy-confusable-chars-gen${ExeSuffix}" `
        -D LLDB_TABLEGEN="C:\a\swift-build\swift-build/BinaryCache/0/bin/lldb-tblgen${ExeSuffix}" `
        -D LLVM_CONFIG_PATH="C:\a\swift-build\swift-build/BinaryCache/0/bin/llvm-config${ExeSuffix}" `
        -D LLVM_EXTERNAL_SWIFT_SOURCE_DIR=C:\a\swift-build\swift-build/SourceCache/swift `
        -D LLVM_NATIVE_TOOL_DIR=C:\a\swift-build\swift-build/BinaryCache/0/bin `
        -D LLVM_TABLEGEN="C:\a\swift-build\swift-build/BinaryCache/0/bin/llvm-tblgen${ExeSuffix}" `
        -D LLVM_USE_HOST_TOOLS=NO `
        -D SWIFT_BUILD_DYNAMIC_SDK_OVERLAY=NO `
        -D SWIFT_BUILD_DYNAMIC_STDLIB=NO `
        -D SWIFT_BUILD_REMOTE_MIRROR=NO `
        -D SWIFT_BUILD_SWIFT_SYNTAX=YES `
        -D SWIFT_CLANG_LOCATION="C:/Users/runneradmin/AppData/Local/Programs/Swift/Toolchains/6.0.0+Asserts/usr/bin" `
        -D SWIFT_ENABLE_EXPERIMENTAL_CONCURRENCY=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_CXX_INTEROP=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_DISTRIBUTED=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_DIFFERENTIABLE_PROGRAMMING=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_OBSERVATION=YES `
        -D SWIFT_ENABLE_EXPERIMENTAL_STRING_PROCESSING=YES `
        -D SWIFT_ENABLE_SYNCHRONIZATION=YES `
        -D SWIFT_NATIVE_SWIFT_TOOLS_PATH=C:\a\swift-build\swift-build/BinaryCache/0/bin `
        -D SWIFT_PATH_TO_LIBDISPATCH_SOURCE=C:\a\swift-build\swift-build/SourceCache/swift-corelibs-libdispatch `
        -D SWIFT_PATH_TO_SWIFT_SYNTAX_SOURCE=C:\a\swift-build\swift-build/SourceCache/swift-syntax `
        -D SWIFT_PATH_TO_STRING_PROCESSING_SOURCE=C:\a\swift-build\swift-build/SourceCache/swift-experimental-string-processing `
        -D SWIFT_PATH_TO_SWIFT_SDK="C:/Users/runneradmin/AppData/Local/Programs/Swift/Platforms/6.0.0/Windows.platform/Developer/SDKs/Windows.sdk/" `
        -D CLANG_VENDOR=compnerd.org `
        -D CLANG_VENDOR_UTI=org.compnerd.dt `
        -D cmark-gfm_DIR=C:\a\swift-build\swift-build/BinaryCache/Library/cmark-gfm-0.29.0.gfm.13/usr/lib/cmake `
        -D LibXml2_DIR=C:\a\swift-build\swift-build/BinaryCache/Library/libxml2-2.11.5/usr/lib/cmake/libxml2-2.11.5 `
        -D PACKAGE_VENDOR=compnerd.org `
        -D SWIFT_VENDOR=compnerd.org `
        -D LLVM_PARALLEL_LINK_JOBS=2 `
        -D SWIFT_PARALLEL_LINK_JOBS=2 `
        -D LLVM_APPEND_VC_REV=NO `
        -D LLVM_VERSION_SUFFIX="" `
        -D LLDB_PYTHON_EXE_RELATIVE_PATH=python.exe `
        -D LLDB_PYTHON_EXT_SUFFIX=.pyd `
        -D LLDB_PYTHON_RELATIVE_PATH=lib/site-packages `
        -D Python3_EXECUTABLE=C:\hostedtoolcache\windows\Python\3.9.10\x64\python.exe `
        -D Python3_INCLUDE_DIR=C:\hostedtoolcache\windows\Python\3.9.10\x64/include `
        -D Python3_LIBRARY=C:\hostedtoolcache\windows\Python\3.9.10\x64/libs/python39.lib `
        -D Python3_ROOT_DIR=$env:pythonLocation