ClangImporter: allow control over ObjCInterop

Select the language for the clang importer based on the
`-enable-objc-interop` flag rather than target.  This paves the road to
enabling ObjC tests on non-Darwin targets as well as building on Darwin
without ObjC interop.

Author: compnerd

lib/ClangImporter/ClangImporter.cpp

@@ -430,7 +430,8 @@ static void
 getNormalInvocationArguments(std::vector<std::string> &invocationArgStrs,
                              ASTContext &ctx,
                              const ClangImporterOptions &importerOpts) {
-  const llvm::Triple &triple = ctx.LangOpts.Target;
+  const auto &LangOpts = ctx.LangOpts;
+  const llvm::Triple &triple = LangOpts.Target;
   SearchPathOptions &searchPathOpts = ctx.SearchPathOpts;
 
   auto languageVersion = ctx.LangOpts.EffectiveLanguageVersion;
@@ -463,12 +464,24 @@ getNormalInvocationArguments(std::vector<std::string> &invocationArgStrs,
       SHIMS_INCLUDE_FLAG, searchPathOpts.RuntimeResourcePath,
   });
 
+  if (LangOpts.EnableObjCInterop)
+    invocationArgStrs.insert(invocationArgStrs.end(),
+                             {"-x", "objective-c", "-std=gnu11", "-fobjc-arc"});
+  else
+    invocationArgStrs.insert(invocationArgStrs.end(), {"-x", "c", "-std=gnu11"});
+
+  // Get the version of this compiler and pass it to C/Objective-C declarations.
+  auto V = version::Version::getCurrentCompilerVersion();
+  if (!V.empty()) {
+    invocationArgStrs.insert(invocationArgStrs.end(), {
+        V.preprocessorDefinition("__SWIFT_COMPILER_VERSION",
+                                 {1000000000, /*ignored*/ 0, 1000000, 1000, 1}),
+    });
+  }
+
   // Set C language options.
   if (triple.isOSDarwin()) {
     invocationArgStrs.insert(invocationArgStrs.end(), {
-      // Darwin uses Objective-C ARC.
-      "-x", "objective-c", "-std=gnu11", "-fobjc-arc",
-
       // Define macros that Swift bridging headers use.
       "-DSWIFT_CLASS_EXTRA=__attribute__((annotate(\""
         SWIFT_NATIVE_ANNOTATION_STRING "\")))",
@@ -513,25 +526,7 @@ getNormalInvocationArguments(std::vector<std::string> &invocationArgStrs,
       // Request new APIs from UIKit.
       "-DSWIFT_SDK_OVERLAY_UIKIT_EPOCH=2",
     });
-
-    // Get the version of this compiler and pass it to
-    // C/Objective-C declarations.
-    auto V = version::Version::getCurrentCompilerVersion();
-    if (!V.empty()) {
-      invocationArgStrs.insert(invocationArgStrs.end(), {
-        V.preprocessorDefinition("__SWIFT_COMPILER_VERSION",
-                                 {1000000000, /*ignored*/0, 1000000, 1000, 1}),
-      });
-    }
   } else {
-    invocationArgStrs.insert(invocationArgStrs.end(), {
-      // Non-Darwin platforms don't use the Objective-C runtime, so they can
-      // not import Objective-C modules.
-      //
-      // Just use the most feature-rich C language mode.
-      "-x", "c", "-std=gnu11",
-    });
-
     // The module map used for Glibc depends on the target we're compiling for,
     // and is not included in the resource directory with the other implicit
     // module maps. It's at {freebsd|linux}/{arch}/glibc.modulemap.