cmd/go: re-enable a couple of tests of gccgo

Port https://golang.org/cl/120375 over to the gofrontend repo so that
it gets more reliable testing.

Updates golang/go#22472

Change-Id: I314396e49934374a143a025a477f01449ac1812b
Reviewed-on: https://go-review.googlesource.com/120395
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
diff --git a/libgo/go/cmd/go/go_test.go b/libgo/go/cmd/go/go_test.go
index f6d6f42..20606d8 100644
--- a/libgo/go/cmd/go/go_test.go
+++ b/libgo/go/cmd/go/go_test.go
@@ -791,7 +791,6 @@
 	tg.run("build", "-x", "-o", os.DevNull, "complex")
 
 	if _, err := exec.LookPath("gccgo"); err == nil {
-		t.Skip("golang.org/issue/22472")
 		tg.run("build", "-x", "-o", os.DevNull, "-compiler=gccgo", "complex")
 	}
 }
@@ -2944,7 +2943,6 @@
 	if _, err := exec.LookPath("gccgo"); err != nil {
 		t.Skip("skipping because no gccgo compiler found")
 	}
-	t.Skip("golang.org/issue/22472")
 
 	tg := testgo(t)
 	defer tg.cleanup()