Android.mk: replace std=c99 with std=gnu99

Android.mk: replace std=c99 with std=gnu99

The android makefiles were passing the -std=c99 flag to the
compiler which disables the typeof keyword. This causes a
build fail for a recent addition to igt_aux.h.
Change this to -std=gnu99, which is the flag used in the
linux build

Signed-off-by: Tim Gore <tim.gore@intel.com>
Signed-off-by: Thomas Wood <thomas.wood@intel.com>