[dev.cc] cmd/go: fix expansion of cmd

This was supposed to be in the previous CL, but I forgot to 'git rw' it down.

Change-Id: Ia5e14ca2c7640f08abbbed1a777a6cf04d71d0e7
Reviewed-on: https://go-review.googlesource.com/5570Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/main.go

@@ -505,7 +505,7 @@ func matchPackages(pattern string) []string {
 	var pkgs []string
 
 	for _, src := range buildContext.SrcDirs() {
-		if pattern == "std" && src != gorootSrc {
+		if (pattern == "std" || pattern == "cmd") && src != gorootSrc {
 			continue
 		}
 		src = filepath.Clean(src) + string(filepath.Separator)