ibacm: support distros with older versions of gcc

ibacm: support distros with older versions of gcc

ibacm implements atomics using gcc intrinsics that were introduced
in gcc 4.1.2.  If an older version of gcc is used to compile the
code, an error results.  Check that the required atomic calls are
supported, and if not, provide our own implementation.

This fixes a build issue on RH 5.x.

Signed-off-by: Sean Hefty <sean.hefty@intel.com>