aarch64: blacklist gcc prior to 5.1

Linux aarch64 requires GCC 5.1 or better because prior versions perform
unsafe access to deallocated stack.

Some Linux distributions may have backported the fix, but it was never
released into earlier upstream gcc versions.

Link: https://lwn.net/Articles/842122/
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>