glog: fix atomic built-in problem

glog can optionally use atomic __sync built-ins. However, its
configure script only checks for the availability of the 4-byte
variant, but the code also uses the 1-byte variant. While this works
on most architectures, it does not on architectures that implement
only the 4-byte variant, such as Microblaze. So if the architecture
does not implement the 1-byte variant, we hint the configure script
that atomic built-ins should not be used.

Fixes:

  http://autobuild.buildroot.org/results/bedebd594c283adf39374c9a9f44432e5d6cbff7/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: "Yann E. MORIN" <yann.morin.1998@free.fr>