Frontend: -disable-clang-target should be a flag

Author: nkcsgexi

include/swift/Option/Options.td

@@ -1070,7 +1070,7 @@ def clang_target : Separate<["-"], "clang-target">,
   Flags<[FrontendOption, SwiftAPIExtractOption, SwiftSymbolGraphExtractOption, SwiftAPIDigesterOption]>,
   HelpText<"Separately set the target we should use for internal Clang instance">;
 
-def disable_clang_target : Separate<["-"], "disable-clang-target">,
+def disable_clang_target : Flag<["-"], "disable-clang-target">,
   Flags<[NewDriverOnlyOption]>,
   HelpText<"Disable a separately specified target triple for Clang instance to use">;