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

cc/util.go

@@ -88,6 +88,7 @@ func moduleToLibName(module string) (string, error) {
 func flagsToBuilderFlags(in Flags) builderFlags {
 	return builderFlags{
 		globalFlags: strings.Join(in.GlobalFlags, " "),
+		arFlags:     strings.Join(in.ArFlags, " "),
 		asFlags:     strings.Join(in.AsFlags, " "),
 		cFlags:      strings.Join(in.CFlags, " "),
 		conlyFlags:  strings.Join(in.ConlyFlags, " "),