RFR: 7181175 Enable hotspot builds on Windows with MinGW/MSYS

[Tim Bell]

I wrote:
> My test build is running now.  I'll update the webrev and send out a 
> new URL.

The test builds were successful.  I also ran full hotspot builds on JPRT 
using '-release jdk8' and '-release jdk7u6', so there is no regression 
in the old builds.  I believe I have addressed the review feedback 
received so far:

  http://cr.openjdk.java.net/~tbell/7181175/webrev.01/

Thanks-

Tim

> http://mail.openjdk.java.net/pipermail/build-dev/2012-March/005729.html
> http://cr.openjdk.java.net/~simonis/MinGW_MSYS_hotspot.v1/