Fix objc link flag being added on non-darwin platforms

driver/linker-gcc.cpp

@@ -715,7 +715,6 @@ void ArgsBuilder::addDefaultPlatformLibs() {
   // fallthrough
   case llvm::Triple::Darwin:
   case llvm::Triple::MacOSX:
-    this->addObjcStdlibLinkFlags(triple);
   case llvm::Triple::FreeBSD:
   case llvm::Triple::NetBSD:
   case llvm::Triple::OpenBSD:
@@ -738,6 +737,13 @@ void ArgsBuilder::addDefaultPlatformLibs() {
     break;
   }
 
+  if (triple.isOSDarwin()) {
+
+    // libobjc is more or less required, so we link against it here.
+    // This could be prettier, though.
+    this->addObjcStdlibLinkFlags(triple);
+  }
+
   if (triple.isWindowsGNUEnvironment()) {
     // This is really more of a kludge, as linking in the Winsock functions
     // should be handled by the pragma(lib, ...) in std.socket, but it