Unix: Use llvm-ar by default

Now that llvm-ar is installed by default in the toolchain, swiftlang/swift#62510,
and a recent SPM change requires there to be an archiver in the toolchain/PATH,
swiftlang/swift-package-manager#5761, use that bundled llvm-ar for all Unix
platforms.

Author: finagolfin

Sources/SwiftDriver/Jobs/GenericUnixToolchain+LinkerSupport.swift

@@ -334,20 +334,15 @@ extension GenericUnixToolchain {
       commandLine.appendPath(outputFile)
       return try resolvedTool(clangTool, pathOverride: clangPath)
     case .staticLibrary:
-      // We're using 'ar' as a linker
+      // We're using 'llvm-ar' as a linker
       commandLine.appendFlag("crs")
       commandLine.appendPath(outputFile)
 
       commandLine.append(contentsOf: inputs.lazy.filter {
                             lto == nil ? $0.type == .object
                                        : $0.type == .object || $0.type == .llvmBitcode
                          }.map { .path($0.file) })
-      if targetTriple.environment == .android {
-        // Always use the LTO archiver llvm-ar for Android
-        return try resolvedTool(.staticLinker(.llvmFull))
-      } else {
-        return try resolvedTool(.staticLinker(lto))
-      }
+      return try resolvedTool(.staticLinker(.llvmFull))
     }
 
   }

Sources/SwiftDriver/Toolchains/GenericUnixToolchain.swift

@@ -66,10 +66,7 @@ public final class GenericUnixToolchain: Toolchain {
     switch tool {
     case .swiftCompiler:
       return try lookup(executable: "swift-frontend")
-    case .staticLinker(nil):
-      return try lookup(executable: "ar")
-    case .staticLinker(.llvmFull),
-         .staticLinker(.llvmThin):
+    case .staticLinker:
       return try lookup(executable: "llvm-ar")
     case .dynamicLinker:
       // FIXME: This needs to look in the tools_directory first.

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -2151,7 +2151,8 @@ final class SwiftDriverTests: XCTestCase {
 
       let linkJob = plannedJobs[3]
       let cmd = linkJob.commandLine
-      // we'd expect "ar crs libTest.a foo.o bar.o"
+      // we'd expect "llvm-ar crs libTest.a foo.o bar.o"
+      XCTAssertTrue(linkJob.tool.name.contains("llvm-ar"))
       XCTAssertTrue(cmd.contains(.flag("crs")))
       XCTAssertTrue(commandContainsTemporaryPath(cmd, "foo.o"))
       XCTAssertTrue(commandContainsTemporaryPath(cmd, "bar.o"))