package/atop: work around gcc bug 85180

With Microblaze Gcc version < 8.x the build hangs due to gcc bug
85180: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85180. The bug
shows up when building atop with optimization but not when building
with -O0. To work around this, if BR2_TOOLCHAIN_HAS_GCC_BUG_85180=y
we force using -O0.

Fixes:

  http://autobuild.buildroot.net/results/94aa00f776b8a3491ac0b3212c95f5e666c5a29a/



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