win: x86 targets XP subsystem

The default in the VS2013 compiler has been switched to Vista+,
however the runtime library still supports XP if the PE header
is set properly. So, make sure the subsystem is set to 5.01 so
that gyp-built binaries can be run on XP.

R=thakis@chromium.org
BUG=chromium:297971

Review URL: https://codereview.chromium.org/68533011

git-svn-id: http://gyp.googlecode.com/svn/trunk@1784 78cadc50-ecff-11dd-a971-7dbc132099af
2 files changed