cmd/compile: skip compiling wrappers for imported defined types

When compiling a package that defines a type T with method T.M, we
already compile and emit the wrapper method (*T).M. There's no need
for every package that uses T to do the same.

Change-Id: I3ca2659029907570f8b98d66111686435fad7ed0
Reviewed-on: https://go-review.googlesource.com/74412
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

src/cmd/compile/internal/gc/subr.go

@@ -1659,6 +1659,12 @@ func genwrapper(rcvr *types.Type, method *types.Field, newnam *types.Sym, iface
 		fmt.Printf("genwrapper rcvrtype=%v method=%v newnam=%v\n", rcvr, method, newnam)
 	}
 
+	// Only generate (*T).M wrappers for T.M in T's own package.
+	if rcvr.IsPtr() && rcvr.Elem() == method.Type.Recv().Type &&
+		rcvr.Elem().Sym != nil && rcvr.Elem().Sym.Pkg != localpkg {
+		return
+	}
+
 	lineno = autogeneratedPos
 
 	dclcontext = PEXTERN