ninja win: Add support for 'CallingConvention'

Each calling convention decorates C functions in a different way, so we can use
that to test the flag.

BUG=
R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/597993003

git-svn-id: http://gyp.googlecode.com/svn/trunk@1984 78cadc50-ecff-11dd-a971-7dbc132099af