RFR: JDK-8079788: Fix broken CL version detection in configure for some Visual Studio configurations

[Erik Joelsson]

Hello,

When building for 32bit with (at least) Visual Studio 2010, configure 
may fail to run with the error:

configure: error: Target CPU mismatch. We are building for x86 but CL is 
for "directory"; expected "80x86" or "x86"

This is caused by cl.exe failing to load mspdb100.dll, which in turn is 
caused by configure throwing away the PATH extracted from the Visual 
Studio setup script after finding the compilers. As I understand it, 
cl.exe is not guaranteed to work unless the PATH is actually setup 
correctly, so we should make sure to keep it correct in configure. (In 
the makefiles, we already export this PATH).

Bug: https://bugs.openjdk.java.net/browse/JDK-8079788

Webrev: http://cr.openjdk.java.net/~erikj/8079788/webrev.01/

/Erik