Enable '-clang-target' by-default

This will result in the driver passing down '-clang-target' flag to the frontend, which will then ensure that all downstream module (Swift and Clang) compilation compiler sub-invocations are consistent with respect to the target triple used by their underlying instances of Clang. Resulting in all Clang module dependencies being built against the main module's target triple.

Author: artemcm

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -74,10 +74,8 @@ extension Driver {
 
     // Pass down -clang-target.
     // If not specified otherwise, we should use the same triple as -target
-    // TODO: enable -clang-target for implicit module build as well.
     if !parsedOptions.hasArgument(.disableClangTarget) &&
-        isFrontendArgSupported(.clangTarget) &&
-        parsedOptions.contains(.driverExplicitModuleBuild) {
+        isFrontendArgSupported(.clangTarget) {
       let clangTriple = parsedOptions.getLastArgument(.clangTarget)?.asSingle ?? targetTriple.triple
       commandLine.appendFlag(.clangTarget)
       commandLine.appendFlag(clangTriple)

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -3622,7 +3622,7 @@ final class SwiftDriverTests: XCTestCase {
     #endif
   }
 
-  func testDisableClangTargetForImplicitModule() throws {
+  func testEnableClangTargetForImplicitModule() throws {
     var envVars = ProcessEnv.vars
     envVars["SWIFT_DRIVER_LD_EXEC"] = ld.nativePathString(escaped: false)
 
@@ -3632,7 +3632,7 @@ final class SwiftDriverTests: XCTestCase {
     let plannedJobs = try driver.planBuild()
     XCTAssertEqual(plannedJobs.count, 2)
     XCTAssert(plannedJobs[0].commandLine.contains(.flag("-target")))
-    XCTAssertFalse(plannedJobs[0].commandLine.contains(.flag("-clang-target")))
+    XCTAssertTrue(plannedJobs[0].commandLine.contains(.flag("-clang-target")))
   }
 
   func testPCHasCompileInput() throws {