Regression: Apple Sillicon support

Hello,

In recent release 1.14.4 you added support for Apple Silicon[0], however, this caused the regression. PIP is not able to build cffi anymore on systems.

Environment:

Red Hat Enterprise Linux Server release 6.6 (Santiago)

gcc-4.4.7-11.el6.x86_64

Error:

    gcc -pthread -DDYNAMIC_ANNOTATIONS_ENABLED=1 -DNDEBUG -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector --param=ssp-buffer-size=4 -m64 -mtune=generic -D_GNU_SOURCE -fPIC -fwrapv -fPIC -DUSE__THREAD -DHAVE_SYNC_SYNCHRONIZE -I/usr/lib64/libffi-3.0.5/include -I/builddir/build/BUILD/migval-1.0.233/venv/include -I/usr/include/python3.4m -c c/_cffi_backend.c -o build/temp.linux-x86_64-3.4/c/_cffi_backend.o
    c/_cffi_backend.c: In function 'b_callback':
    c/_cffi_backend.c:6344: error: #pragma GCC diagnostic not allowed inside functions
    c/_cffi_backend.c:6345: error: #pragma GCC diagnostic not allowed inside functions
    c/_cffi_backend.c:6352: error: #pragma GCC diagnostic not allowed inside functions
    error: command 'gcc' failed with exit status 1

[0] 89bbed80be4d