Request for Review: Add hotspot support for building with mingw/msys on build-infra (the new build)

[Magnus Ihse Bursie]

The following patch will allow build-infra to perform builds on MinGW/MSys.

It also updates the case for cygwin, with the two changes:

1) It replaces a $(subst) from / to \ which acted on output from cygpath 
-m (mixed mode), with just cygpath -w (windows mode, i.e. mixed mode but 
with \ instead of /).

2) In analogy with the msys case, we only do path convertion of the 
first word (i.e. the executable), not any possibly following arguments. 
In reality, there are no argument in the cygwin case (in contrary to the 
msys case, where the build infra solution requires passing additional 
arguments to the binaries).

If these are problematic, they can be dropped. The important part, from 
build-infras point of view, is the mingw case.

http://cr.openjdk.java.net/~ihse/hotspot-build-infra-msys-support/webrev.00/

/Magnus