Allow custom ar flags to be set.

Adds the ability to set custom flags for ar in Soong, similar to how
they can currently be set for make.

Bug: 36290748
Test: sanitize.go is able to correct set custom ar flags for CFI. CFI
enabled Soong components build and boot without issue.

Change-Id: I3212793aa84ba51df910c184d8bb376b3650376e
diff --git a/cc/builder.go b/cc/builder.go
index 9a871d5..f3a4bcb 100644
--- a/cc/builder.go
+++ b/cc/builder.go
@@ -184,6 +184,7 @@
 
 type builderFlags struct {
 	globalFlags string
+	arFlags     string
 	asFlags     string
 	cFlags      string
 	conlyFlags  string
@@ -367,6 +368,9 @@
 
 	arCmd := gccCmd(flags.toolchain, "ar")
 	arFlags := "crsPD"
+	if flags.arFlags != "" {
+		arFlags += " " + flags.arFlags
+	}
 
 	ctx.ModuleBuild(pctx, android.ModuleBuildParams{
 		Rule:      ar,