Make sure git cache dir is not referenced directly in case of cygwin.
Make sure git cache dir is not referenced directly in case of cygwin.

No directories can be directly referenced inside of git commands since
cygwin directories can be different. Use the directory as a cwd of the
command instead.

BUG= None
TEST= toolchain_build trybots
R=bradnelson@google.com

Review URL: https://codereview.chromium.org/322263002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13321 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

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