Workaround bug 338633. gdbserver_tests/nlcontrolc.vgtest hangs on arm64.

Disable the test on arm64 for now to keep make regtest from hanging.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14376 a5019735-40e9-0310-863c-91ae7b9d1cf9