GCC atomic sync usage

Change the check for GCC atomic intrinsics based on GCC version so that
it works on both x86 and Tile architecture. Any GCC after 4.1 has the
__sync_ intrinsics.
Increase size of some atomic variables for better performance.

The Tile-Gx architecture has native support for 32-bit and 64-bit
atomic operations, but not 8-bit and 16-bit, which are emulated, so
changing some 16-bit and 8-bit atomic into ints improves performance.

Increasing the size of the atomic variables modified in this change
does not increase the total size of the structures in which they
reside because of existing padding requirements.