RFR: JDK-8035751 Clean up Visual Studio detection logic

Mon Mar 24 11:04:31 UTC 2014

This bug was triggered by the issue in JDK-8035725. Had the VS detection 
logic been more transparent, that bug would not have had to happen.

We need to rewrite the VS detection so that it is much more controlled, 
and do not run an unchecked shell script that modifies arbitrary 
environment variables. We can never re-create the same circumstances 
during "make time" as we have during "configure time" in that case. 
Instead, we should systematically set only those variables that are 
actually needed.

Bug: https://bugs.openjdk.java.net/browse/JDK-8035751
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8035751-clean-up-visual-studio-detection/webrev.01

/Magnus