Use dependency tags for genrules

So that we don't get confused when using :<module> in srcs to depend on
a module that could also be a HostBinTool.

Test: m -j
Change-Id: Ia3b1c26826e70f84c6dc5ff78c95dd11d76901b6
diff --git a/cc/cc.go b/cc/cc.go
index fe9c4a4..f0ba1c6 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -956,6 +956,7 @@
 		if cc == nil {
 			switch tag {
 			case android.DefaultsDepTag, android.SourceDepTag:
+				// Nothing to do
 			case genSourceDepTag:
 				if genRule, ok := m.(genrule.SourceFileGenerator); ok {
 					depPaths.GeneratedSources = append(depPaths.GeneratedSources,