Support multilib property for cc_genrule

Change genrule Out to `android:"arch_variant"` for supporting
multilib variants.

Bug: 323295272
Test: go test -run TestMultilibGenruleOut

Change-Id: I102d64b45a5a2a5193f813001fc32da0d1fe9d36
diff --git a/genrule/genrule.go b/genrule/genrule.go
index 6f66088..17e97b6 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -808,7 +808,7 @@
 
 type genRuleProperties struct {
 	// names of the output files that will be generated
-	Out []string
+	Out []string `android:"arch_variant"`
 }
 
 var Bool = proptools.Bool