[AST] Factor out a LangOptions-independent helper for isActivePlatform(). NFC.

This will be used in a later commit.

Author: devincoughlin

lib/AST/PlatformKind.cpp

@@ -56,35 +56,43 @@ Optional<PlatformKind> swift::platformFromString(StringRef Name) {
       .Default(Optional<PlatformKind>());
 }
 
-bool swift::isPlatformActive(PlatformKind Platform, LangOptions &LangOpts) {
+static bool isPlatformActiveForTarget(PlatformKind Platform,
+                                      const llvm::Triple &Target,
+                                      bool EnableAppExtensionRestrictions) {
   if (Platform == PlatformKind::none)
     return true;
 
   if (Platform == PlatformKind::OSXApplicationExtension ||
       Platform == PlatformKind::iOSApplicationExtension)
-    if (!LangOpts.EnableAppExtensionRestrictions)
+    if (!EnableAppExtensionRestrictions)
       return false;
 
   // FIXME: This is an awful way to get the current OS.
   switch (Platform) {
     case PlatformKind::OSX:
     case PlatformKind::OSXApplicationExtension:
-      return LangOpts.Target.isMacOSX();
+      return Target.isMacOSX();
     case PlatformKind::iOS:
     case PlatformKind::iOSApplicationExtension:
-      return LangOpts.Target.isiOS() && !LangOpts.Target.isTvOS();
+      return Target.isiOS() && !Target.isTvOS();
     case PlatformKind::tvOS:
     case PlatformKind::tvOSApplicationExtension:
-      return LangOpts.Target.isTvOS();
+      return Target.isTvOS();
     case PlatformKind::watchOS:
     case PlatformKind::watchOSApplicationExtension:
-      return LangOpts.Target.isWatchOS();
+      return Target.isWatchOS();
     case PlatformKind::none:
       llvm_unreachable("handled above");
   }
   llvm_unreachable("bad PlatformKind");
 }
 
+bool swift::isPlatformActive(PlatformKind Platform, LangOptions &LangOpts) {
+  llvm::Triple TT = LangOpts.Target;
+  return isPlatformActiveForTarget(Platform, TT,
+                                   LangOpts.EnableAppExtensionRestrictions);
+}
+
 PlatformKind swift::targetPlatform(LangOptions &LangOpts) {
   if (LangOpts.Target.isMacOSX()) {
     return (LangOpts.EnableAppExtensionRestrictions