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
    
    Reviewed-on: https://go-review.googlesource.com/120395

From-SVN: r261871

gcc/go/gofrontend/MERGE

@@ -1,4 +1,4 @@
-c3ef5bbf4e4271216b6f22621269d458599e8087
+d3eb93c1b8990dbfd4bb660c5c8454916b62655c
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

libgo/go/cmd/go/go_test.go

@@ -791,7 +791,6 @@ func TestBuildComplex(t *testing.T) {
 	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 @@ func TestIssue7573(t *testing.T) {
 	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()