[CMake] cmake and MINGW's ld.exe issue

[Dick Eimers]

I have a CMakeList.txt file for a small project which works when
generating a MSVC 2005 project/solution, but does not work when I
generate Unix Makefiles used with MINGW. When using these makefiles
within MINGW, cmake is able to figure out my MINGW g++ compiler and
linker *but* when 'make'ing it failes due to a 

"c:\mingw\bin\..\lib\gcc\mingw32\3.4.2\..\..\..\..\mingw32\bin\ld.exe:
 cannot find -lgtkmm-2.4.lib "

When executing 'ld.exe -L/path/to/libs -lgtkmm-2.4.lib' I get the same
message, it can be solved by removing the '.lib' part.. 

Can anyone shed some light on this?