[CMake] IF(LINUX) don't work

[Brad King]

Christian Ehrlicher wrote:
> Sorry, what's the difference between WIN32 and MINGW? And why do you want
> WIN32 instead of WINDOWS?

The name WIN32 instead of WINDOWS is historical, just like _WIN32 is 
defined by MS compilers even on 64-bit windows.  I've made a note to add 
WINDOWS.

When building with a MinGW compiler the name MINGW is true as well as 
WIN32.  If you look back through this list's archives you may find some 
big discussions about whether MinGW is different from Windows.  If you 
don't want your project to treat them differently then just don't ever 
test for MINGW.

-Brad