ninja windows: keep cc as something valid for c99conv
ninja windows: keep cc as something valid for c99conv

Keep "cc = cl.exe" around because c99conv uses it to try to find what it
should use to preprocess. It should probably be passed this somehow else
instead.

R=thakis@chromium.org
BUG=233985

Review URL: https://codereview.chromium.org/14145005
old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google