win: disable stl exception usage

Tell the stl that exception handling is unavailable. This avoids warnings
like:

  C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\
  xlocale(337): warning C4530: C++ exception handler used, but unwind
  semantics are not enabled. Specify /EHsc

PR-URL: https://github.com/iojs/io.js/pull/258


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>