Add Ninja support for MSVS $(TargetExt), $(TargetFileName) and $(TargetPath) macros.

BUG=gyp:462
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/629543002

git-svn-id: http://gyp.googlecode.com/svn/trunk@1988 78cadc50-ecff-11dd-a971-7dbc132099af