Rustdoc support.

Adds `m rustdoc` which generates documentation for all Rust libraries
to $OUT_DIR/soong/rustdoc.

Follow up work:

* Generate an index page that lists all modules.
* Preserve the artifacts so we can have an always-up-to-date go link.

Test: m rustdoc
Bug: None
Change-Id: Id2d6b9cbab5b02e36b575567563d7cc7606b9401
diff --git a/rust/proc_macro.go b/rust/proc_macro.go
index 115045a..4eead32 100644
--- a/rust/proc_macro.go
+++ b/rust/proc_macro.go
@@ -68,7 +68,7 @@
 	outputFile := android.PathForModuleOut(ctx, fileName)
 
 	srcPath, _ := srcPathFromModuleSrcs(ctx, procMacro.baseCompiler.Properties.Srcs)
-	TransformSrctoProcMacro(ctx, srcPath, deps, flags, outputFile, deps.linkDirs)
+	TransformSrctoProcMacro(ctx, srcPath, deps, flags, outputFile)
 	return outputFile
 }