Allow cc_genrule srcs to vary by architecture

Add arch_variant to the genrule srcs property so that cc_genrule
modules can vary the srcs and outs by architecture.

Test: cc/genrule_test.go
Change-Id: Idb17013e137d7ca21ca4cfc3e4c1fa7d89977043
diff --git a/genrule/genrule_test.go b/genrule/genrule_test.go
index 7e16ce1..a99fa18 100644
--- a/genrule/genrule_test.go
+++ b/genrule/genrule_test.go
@@ -27,7 +27,7 @@
 
 func setUp() {
 	var err error
-	buildDir, err = ioutil.TempDir("", "soong_java_test")
+	buildDir, err = ioutil.TempDir("", "genrule_test")
 	if err != nil {
 		panic(err)
 	}