package/lmbench: fix build failure due to gcc bug 101915

The lmbench package exhibits gcc bug 101915 when built for the
Microblaze 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_101915=y.

Fixes:
http://autobuild.buildroot.net/results/ae1/ae1e4d61ed367c6cb64442c60d98882cc7985346/

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

package/lmbench/lmbench.mk

@@ -18,6 +18,10 @@ LMBENCH_CFLAGS += `$(PKG_CONFIG_HOST_BINARY) --cflags libtirpc`
 LMBENCH_LDLIBS = `$(PKG_CONFIG_HOST_BINARY) --libs libtirpc`
 endif
 
+ifeq ($(BR2_TOOLCHAIN_HAS_GCC_BUG_101915),y)
+LMBENCH_CFLAGS += -O0
+endif
+
 LMBENCH_POST_PATCH_HOOKS += UPDATE_CONFIG_HOOK
 
 define LMBENCH_CONFIGURE_CMDS