win msvs: make express editions not use x64-x64 compiler

VS2012 express and others do not include a 64 bit compiler
that generates 64 bit code. This patch makes it so the
64 bit compiler is only enabled when not using a Visual
Studio express edition.

Patch from david@sankelsoftware.com.

R=scottmg@chromium.org

Review URL: https://codereview.chromium.org/101223013

git-svn-id: http://gyp.googlecode.com/svn/trunk@1829 78cadc50-ecff-11dd-a971-7dbc132099af