Make generated_sources act like generated_headers

Make generated_sources dependencies honor the exported include
directories.

Test: m -j checkbuild
Change-Id: I6955cf5d985053071c2118f43fa1accdb4cc27ab
diff --git a/cc/cc.go b/cc/cc.go
index 6e2f6a5..bbdcf6f 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -907,6 +907,8 @@
 				} else {
 					ctx.ModuleErrorf("module %q is not a gensrcs or genrule", name)
 				}
+				// Support exported headers from a generated_sources dependency
+				fallthrough
 			case genHeaderDepTag, genHeaderExportDepTag:
 				if genRule, ok := m.(genrule.SourceFileGenerator); ok {
 					depPaths.GeneratedHeaders = append(depPaths.GeneratedHeaders,