Specify module dependency in the srcs list

* "srcs" list contains one main Rust source file,
  followed by optional dependent modules.
* A dependent module included in the "srcs" list is
  the module name prefixed with ":".
* Add a simple test.

Bug: 160331255
Test: make and manual test build dependencies on genrule modules
Change-Id: I4f079138c2599158810b6412fce81b612a3f64a4
diff --git a/rust/builder.go b/rust/builder.go
index 16d7306..7f94bb5 100644
--- a/rust/builder.go
+++ b/rust/builder.go
@@ -166,6 +166,7 @@
 	implicits = append(implicits, rustLibsToPaths(deps.ProcMacros)...)
 	implicits = append(implicits, deps.StaticLibs...)
 	implicits = append(implicits, deps.SharedLibs...)
+	implicits = append(implicits, deps.SrcDeps...)
 	if deps.CrtBegin.Valid() {
 		implicits = append(implicits, deps.CrtBegin.Path(), deps.CrtEnd.Path())
 	}