gpsd: add work-around and re-enable for microblaze

Fix (works around) bug #6872
https://bugs.busybox.net/show_bug.cgi?id=6872

The gpsd package was disabled due to an internal compiler error for
the microblaze architecture in the following commit:
http://git.buildroot.net/buildroot/commit/?id=d517415bcda380336f4a27bf248cef4d81791c9e



The problem is due to an specific GCC optimization flag
(-fexpensive-optimizations), so disabling it we can work around this
problem and compile gpsd for the microblaze architecture.

Signed-off-by: Sergio Prado <sergio.prado@e-labworks.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>