runtime: skip TestGcSys on Windows

This is causing failures on TryBots and BuildBots:
--- FAIL: TestGcSys (0.06s)
    gc_test.go:27: expected "OK\n", but got "using too much memory: 39882752 bytes\n"
FAIL

Updates #27156

Change-Id: I418bbec89002574cd583c97422e433f042c07492
Reviewed-on: https://go-review.googlesource.com/130875
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/gc_test.go

@@ -21,6 +21,9 @@ func TestGcSys(t *testing.T) {
 	if os.Getenv("GOGC") == "off" {
 		t.Skip("skipping test; GOGC=off in environment")
 	}
+	if runtime.GOOS == "windows" {
+		t.Skip("skipping test; GOOS=windows http://golang.org/issue/27156")
+	}
 	got := runTestProg(t, "testprog", "GCSys")
 	want := "OK\n"
 	if got != want {