Pass-down -clang-target to all frontend jobs

Author: nkcsgexi

Sources/SwiftDriver/Jobs/FrontendJobHelpers.swift

@@ -66,6 +66,14 @@ extension Driver {
       }
     }
 
+    // Pass down -clang-target.
+    // If not specified otherwise, we should use the same triple as -target
+    if isFrontendArgSupported(.clangTarget) {
+      let clangTriple = parsedOptions.getLastArgument(.clangTarget)?.asSingle ?? targetTriple.triple
+      commandLine.appendFlag(.clangTarget)
+      commandLine.appendFlag(clangTriple)
+    }
+
     // If in ExplicitModuleBuild mode and the dependency graph has been computed, add module
     // dependencies.
     // May also be used for generation of the dependency graph itself in ExplicitModuleBuild mode.

Tests/SwiftDriverTests/SwiftDriverTests.swift

@@ -2439,6 +2439,15 @@ final class SwiftDriverTests: XCTestCase {
     }
   }
 
+  func testClangTarget() throws {
+    var driver = try Driver(args: ["swiftc", "foo.swift"])
+    let plannedJobs = try driver.planBuild()
+    XCTAssertEqual(plannedJobs.count, 2)
+    XCTAssert(plannedJobs[0].commandLine.contains(.flag("-target")))
+    XCTAssert(plannedJobs[0].commandLine.contains(.flag("-clang-target")))
+    XCTAssert(plannedJobs[1].commandLine.contains(.flag("-target")))
+    XCTAssert(plannedJobs[1].commandLine.contains(.flag("-clang-target")))
+  }
 
   func testPCHasCompileInput() throws {
     var driver = try Driver(args: ["swiftc", "-target", "x86_64-apple-macosx10.14", "-enable-bridging-pch", "-import-objc-header", "TestInputHeader.h", "foo.swift"])