runtime: disable GDB tests on freebsd on all GOARCH values

The in-tree GDB is too old (6.1.1) on all the builders except the
FreeBSD 12.0 one, where it was removed from the base system.

Update #29508

Change-Id: Ib6091cd86440ea005f3f903549a0223a96621a6f
Reviewed-on: https://go-review.googlesource.com/c/156717Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/runtime-gdb_test.go

@@ -39,9 +39,7 @@ func checkGdbEnvironment(t *testing.T) {
 	case "aix":
 		t.Skip("gdb does not work on AIX; see https://golang.org/issue/28558")
 	case "freebsd":
-		if runtime.GOARCH == "arm" {
-			t.Skip("skipping gdb tests on freebsd/arm; see https://golang.org/issue/29508")
-		}
+		t.Skip("skipping gdb tests on FreeBSD; see https://golang.org/issue/29508")
 	}
 	if final := os.Getenv("GOROOT_FINAL"); final != "" && runtime.GOROOT() != final {
 		t.Skip("gdb test can fail with GOROOT_FINAL pending")