package/haproxy: re-enable package on microblaze

package/haproxy: re-enable package on microblaze

With Microblaze ccc version < 8.x and optimization, the build fails
with;

  'internal compiler error: in do_output_reload, at reload1.c:7978'

This is due to gcc bug 90620:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90620. To avoid this, the
haproxy package has a !BR2_microblaze dependency. However, this gcc
bug 90620 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 similar Microblaze issues.

So, this commit passes -O0 when BR2_TOOLCHAIN_HAS_GCC_BUG_90620, and
re-enables haproxy on Microblaze.

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