toolchain: only take last found libgcc* file

toolchain: only take last found libgcc* file

The current $(wildcard ...) match might return multiple files which will break subsequent cp commands
with an error like:

  cp: target `/home/user/openwrt/staging_dir/target-mips_34kc_uClibc-0.9.33.2/root-ar71xx/tmp-libc/lib/libgcc_s_pic.a' is not a directory

Prevent this issue by only taking the last path returned by globbing.

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
SVN-Revision: 41357