package/git: fix build failure due to gcc bug 93847

package/git: fix build failure due to gcc bug 93847

The git package exhibits gcc bug 93847 when built for the Nios2
architecture with optimization enabled, which causes a build failure.

As done for other packages in Buildroot work around this gcc bug by
setting optimization to -O0 if BR2_TOOLCHAIN_HAS_GCC_BUG_93847=y.

Fixes:
http://autobuild.buildroot.net/results/e225e62ea2d48660df4110790664f0c3306c1ea9/

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