[Cmake] How detect build for.

[klaas.holwerda]

Hi,

A simple question, how do i know when VisualC is used, or is there a 
variable that contains
the choosen "Build For:"

( I found BORLAND and CYGWIN ), but WIN32 is not specific enough it 
looks like.

Another might be CMAKE_CXX_COMPILER == cl,
but i assume there most be something more specific?

Thanks for some help,

Klaas