runtime: skip flaky TestGdbPythonCgo on MIPS

It seems the problem is on gdb and the dynamic linker. Skip the
test for now until we figure out what's going on with the system.

Updates #18784.

Change-Id: Ic9320ffd463f6c231b2c4192652263b1cf7f4231
Reviewed-on: https://go-review.googlesource.com/36250
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/runtime-gdb_test.go

@@ -89,6 +89,9 @@ func TestGdbPython(t *testing.T) {
 }
 
 func TestGdbPythonCgo(t *testing.T) {
+	if runtime.GOARCH == "mips" || runtime.GOARCH == "mipsle" {
+		testenv.SkipFlaky(t, 18784)
+	}
 	testGdbPython(t, true)
 }