PNaCl: Override LLVM's git repository detection
PNaCl: Override LLVM's git repository detection

Since we started using a git cache, the URL in pnacl-clang's -v output
has contained a buildbot filesystem URL instead of our real git URL,
which isn't useful, may cause escaping issues on Windows, and prevents
goma from getting cache hits because the output of pnacl-clang -v isn't
the same on different platforms.

BUG= https://code.google.com/p/chromium/issues/detail?id=387514
R=dyen@chromium.org

Review URL: https://codereview.chromium.org/349323002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13392 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client