mesa3d: fix build with gcc <= 4.7 on some architectures

The configure.ac check for atomic intrinsics assumes that if an atomic
intrinsic is not available, it's because we must link with
libatomic. Except that libatomic is not always available, for example
with gcc <= 4.7.

To fix this, this commit adds a patch that reworks the atomic check in
configure.ac. It has been submitted upstream, and tested in a number
of different combinations.

Fixes:

  http://autobuild.buildroot.net/results/b045488d880a4013ed82937e7115b7636867e01d/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>