RFR: JDK-8146403: Windows build can be faster

[Tim Bell]

Erik:

> During the hotspot makefile conversion, we have been reminded of 
> inefficiencies when running make in Cygwin.

> [... snip ...]

> Since these improvements affect much more than just the new hotspot 
> build, I intend to push this to JDK 9 directly.
>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8146403
> Webrev: http://cr.openjdk.java.net/~erikj/8146403/webrev.01/

Looks good to me.  Thanks for doing this.

Tim