tools/Makefile: Get gcc copyright files from Git checkout instead of third_party
tools/Makefile: Get gcc copyright files from Git checkout instead of third_party

This will allow us to remove third_party/gcc from DEPS.

BUG=http://code.google.com/p/nativeclient/issues/detail?id=1132
TEST=run "make SDKLOC=`pwd`/sdk-dest" upto binutils build, and look at
  the output dir

Review URL: http://codereview.chromium.org/6542054

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@4367 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client