Fix for the alignment calculation of anonymous and zero sized bitfields on ARM - Part 2
Created originally on Bitbucket by David Schneider
Was already merged in Bitbucket before import, marked as merged by the import user
This PR does two things:
- It changes the check for ARM in c/_cffi_backend.c to use a flag like it is done for MSVC.
- It adds tests for the bitfield behavior on ARM in c/test_c.py