package/grpc: add workaround for gcc<5

Fixes:
http://autobuild.buildroot.net/results/3d5/3d5e0b2b8c6670cf9a43ceac4b8173760e1f933c/

Commit e0e54afd0cf7 (package/grpc: bump to version 1.25.0) bumped the grpc
version and added a workaround for 'failure memory model cannot be stronger
than success memory model for '__atomic_compare_exchange'.  This workaround
is also needed for 1.23.0, so add it here as well.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
1 file changed