Fix toolchain_build driver installation on windows
Fix toolchain_build driver installation on windows

TBR=bradnelson@google.com
BUG= https://code.google.com/p/nativeclient/issues/detail?id=3719

Review URL: https://codereview.chromium.org/83433007

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@12444 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

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