runtime: disable gdb test when a GOROOT_FINAL move is pending

Fixes #13577.

Change-Id: I0bb8157d6210b0c7c09380c2163b7d7349495732
Reviewed-on: https://go-review.googlesource.com/17970Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/runtime/runtime-gdb_test.go

@@ -60,6 +60,9 @@ func TestGdbPython(t *testing.T) {
 	if runtime.GOOS == "darwin" {
 		t.Skip("gdb does not work on darwin")
 	}
+	if final := os.Getenv("GOROOT_FINAL"); final != "" && runtime.GOROOT() != final {
+		t.Skip("gdb test can fail with GOROOT_FINAL pending")
+	}
 
 	checkGdbPython(t)