glob: Silence warning about void pointer arithmetic

Sync with gnulib 0e14f025d2.

Checked on x86_64-linux-gnu.

	* lib/glob.c (glob): Use a 'char *', not a 'void *', in pointer
	arithmetic.

Signed-off-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>