package/harfbuzz: work around arc gcc10 bug

With BR2_GCC_VERSION_ARC=y(arc gcc10) harfbuzz package exhibits a gcc bug
that makes build to fail. This bug is found only in official arc gcc10
provided by Synopsis, so we can't use the BR2_TOOLCHAIN_HAS_GCC_BUG_
approach since bug can't be even filed in gcc bugzilla.
To work around this, if BR2_GCC_VERSION_ARC=y we force using -O0.

Fixes:
http://autobuild.buildroot.net/results/e4d/e4da9ba40c8f4567601d404e20dd6a0b322210c2/



Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>