package/assimp: re-enable package on Microblaze

With Microblaze ccc version < 8.x the build hangs due to bug 85180:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85180

. To avoid this, the
assimp package has a !BR2_microblaze dependency. However, gcc bug
85180 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.

So, this commit passes -O0 when BR2_TOOLCHAIN_HAS_GCC_BUG_85180, and
re-enables assimp on Microblaze.

Note that the comment was talking about gcc bug 71124, but this gcc
bug is a duplicate of 85180. Since all Buildroot packages now use the
reference to gcc bug 85180 and the option is named
BR2_TOOLCHAIN_HAS_GCC_BUG_85180, we use this naming as well for
assimp.

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