[NFC][CMake] Disable use of in-process 'libSwiftScan' queries when building the Standard Library

Due to the ordering of our build system, we may encounter a race when building standard library variants using tools produced by Swift's 'tools' CMake build.
As a workaround, for now, ensure that the compiler building standard library variants does not rely on libSwiftScan built as part of 'tools'.

Author: artemcm

stdlib/public/core/CMakeLists.txt

@@ -294,6 +294,11 @@ elseif(SWIFT_PRIMARY_VARIANT_SDK STREQUAL "WINDOWS")
   list(APPEND swift_core_private_link_libraries shell32;DbgHelp;Synchronization)
 endif()
 
+# There is a race condition with building the 'tools' CMake build of the compiler,
+# which produces libSwiftScan that the compiler building the standard library may attempt to use. 
+# Since the current build system makes establishing this dependency relationship exceedingly difficult,
+# we attempt to work around it by disabling use of 'libSwiftScan' here.
+list(APPEND swift_stdlib_compile_flags "-nonlib-dependency-scanner")
 if(NOT "${CMAKE_BUILD_TYPE}" STREQUAL "MinSizeRel")
   list(APPEND swift_stdlib_compile_flags "-Xllvm" "-sil-inline-generics")
   list(APPEND swift_stdlib_compile_flags "-Xllvm" "-sil-partial-specialization")
@@ -439,7 +444,7 @@ if(SWIFT_SHOULD_BUILD_EMBEDDED_STDLIB)
       GYB_SOURCES ${SWIFTLIB_EMBEDDED_GYB_SOURCES}
       SWIFT_COMPILE_FLAGS
         ${swift_stdlib_compile_flags} -Xcc -D__MACH__ -Xcc -D__APPLE__ -Xcc -ffreestanding -enable-experimental-feature Embedded
-        -Xfrontend -enable-ossa-modules
+        -Xfrontend -enable-ossa-modules -nonlib-dependency-scanner
       MODULE_DIR "${CMAKE_BINARY_DIR}/lib/swift/embedded"
       SDK "embedded"
       ARCHITECTURE "${arch}"