nacl-clang driver: Use GetLinkerPath utility function to find linker

This makes it more constistent with other targets and also makes the
-fuse-ld flag work.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4088
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/1183853004.
1 file changed