CEGUI 0.7.x is incapable of detecting DevIL in a MinGW environment.

So on Win32, we will just use FreeImage instead. However, FreeImage
segfaults when you use another libpng/libjpeg/etc. than the one
FreeImage was compiled against. So this works in the limited MXE
environment we use for crosscompilation, but not if you don’t
have absolute control over all libraries used (i.e. compiled them
all yourself).