[Cmake] MinGw support

[Bill Hoffman]

Hi all,

Recently I checked in some changes to CMake that allow the windows binary of CMakeSetup
to generate Unix style makefiles.   This allows for CMakeSetup to be used to generate
makefiles that will work with the gcc/make that comes with MinGw.  I was able
to build VTK with MinGW after a few changes to the CMakeLists.txt files.   
A new predefined variable is now in CMake, called MINGW.   
It can be used for conditional compilation of files:

IF(MINGW)
...
ENDIF(MINGW)


The Unix makefile generator can be used to do some other interesting combinations:

microsoft cl with cygwin gnu make

borland bcc32 with cygwin gnu make

cygwin gcc builds with CMakeSetup and not ccmake-  (There are some issues here,
CMakeSetup is not able to find any of the installed stuff for cygwin in /usr/local
because it is a windows binary and does not understand cygwin paths.)

I expect to put this into CMake 1.8.1.   If you are interested in any of the above,
and can build CMakeSetup from CVS CMake (you will need visual studio 6 or 7),
I would appreciate any feedback or problems before I put it into CMake 1.8.1.

Thanks.

-Bill