undefined reference to `__aarch64_cas4_sync' error on arm64 native build

[richard clark]

Hi Segher,

A ported driver in linux kernel calls '__sync_val_compare_and_swap',
the cross-compiler 'aarch64-linux-gnu-gcc' doesn't complain
'__aarch64_cas1_sync' undefined reference, but the native compiler
will complain. As Mark mentioned, I double check that both cross and
native compiler should have  ''-moutline-atomics' option enabled, do
you know the reason for that?