Revert "Add external projects only CFlags option"

This reverts commit 6a350878d8.

Reason for revert: Breakage of many AOSP targets

Change-Id: I917e6daa04ac02ecb98c7bb1816f9bdaf46429f5

cc/compiler.go

@@ -392,12 +392,6 @@ func (compiler *baseCompiler) compilerFlags(ctx ModuleContext, flags Flags, deps
 			fmt.Sprintf("${config.%sGlobalCflags}", hod))
 	}
 
-	if flags.Clang {
-		if strings.HasPrefix(android.PathForModuleSrc(ctx).String(), "external/") {
-			flags.GlobalFlags = append([]string{"${config.ClangExternalCflags}"}, flags.GlobalFlags...)
-		}
-	}
-
 	if ctx.Device() {
 		if Bool(compiler.Properties.Rtti) {
 			flags.CppFlags = append(flags.CppFlags, "-frtti")