package/libnss: re-enable package on microblaze

package/libnss: re-enable package on microblaze

With Microblaze Gcc version < 8.x the build hangs due to bug 85862:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85862
To avoid this, the libnss package has a !BR2_TOOLCHAIN_HAS_GCC_BUG_85862
dependency. However, gcc bug 85862 only triggers when optimization is
enabled, so we can work around the issue by passing -O0, which is what
we do in other Buildroot packages to work around this bug.

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>