gcc: Update patch to only patch files once

This fixes an error in do_patch when using "PATCHTOOL = "patch""

error message:
checking file gcc/configure.ac Hunk #1 FAILED at 6602.

Signed-off-by: Wang Mingyu <wangmy@cn.fujitsu.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>