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

[Tim Bell]

Erik:

> 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/

Looks good to me.

Tim