Windows build problems

[Daniel Fischer]

I'm trying to set up a build/test environment on Windows.

Building ghc (sh validate) fails after a while due to flex and bison 
crashing. Those two come with git and even
$ flex --version
(or bison) crashes, so they seem truly hosed.

Do I need flex/bison at all to build ghc?
It seems they're not used on linux for building ghc.
So, if not, how do I configure things that the build doesn't try to use 
bison/flex?
If yes, would installing flex and bison from gnuwin32 work?