package/glog: disable on microblaze

Disable glog on microblaze instead of trying to fix the build failure
due to __ELF__ being undefined on this architecture following Arnout
request during review of https://patchwork.ozlabs.org/patch/1186107

Fixes:
 - http://autobuild.buildroot.org/results/ae138c08361d3544df92f88edf3f6dcd617b6232



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>