MinGW and why Linux users should care

Since CMake 2.4.1 I think lower case commands are supported, and since
2.6.0 using all-lowercase is recommended.

Beside that, I can recommend the same: don't try to run executables
during the configure-step, in general this doesn't work for cross
compiling. If cmake recognizes that a cross-compiled executable should be
executed, it doesn't execute it, prints a warning, and writes a file for
setting the result-variables, with hopefully enough comments so this
becomes doable for the developer. Also the cross compiled executables are
kept so the developer can take them, execute them on the target platform
and enter the results manually in that file. That file can then be fed
into cmake using the -C argument.

Alex