Fix llvm-ar error caused by using lto and sanitizer together

LLVM-AR does not allow passing --plugin options more than once. The
--plugin ARFLAGS that lto want to add, may already exist if sanitizer is
also turned on.

Fixed this by adding a new bool Flags.ArGoldPlugin. Set this variable to
true whenever LLVM gold plugin is needed for ArFlags. In function
TransformObjToStaticLib(), add this option to arFlags using global value
${config.LLVMGoldPlugin} if the bool value is true.

Bug: http://b/73160350
Test: build the image with make and succeeded.

Change-Id: I62785829b0a4b663225926e4aed98defc1b6da2c
(cherry picked from commit 4917049f6e)

cc/builder.go

@@ -256,6 +256,7 @@ type builderFlags struct {
 	systemIncludeFlags string
 
 	groupStaticLibs bool
+	arGoldPlugin    bool
 
 	stripKeepSymbols       bool
 	stripKeepMiniDebugInfo bool
@@ -512,6 +513,9 @@ func TransformObjToStaticLib(ctx android.ModuleContext, objFiles android.Paths,
 	if !ctx.Darwin() {
 		arFlags += " -format=gnu"
 	}
+	if flags.arGoldPlugin {
+		arFlags += " --plugin ${config.LLVMGoldPlugin}"
+	}
 	if flags.arFlags != "" {
 		arFlags += " " + flags.arFlags
 	}