[CMake] What folders does "CHECK_INCLUDE_FILES" look into?

[Mathias Bauer]

Hi list,

I'm wandering why a particular header file (pthread.h) is found by CMake 
on one platform, but not on another, though the header file is present 
in the same folder on both of them.

There is no visible difference in how CMake is called, so how can this 
difference be explained? I had a look into the macro implementation, but 
couldn't spot an obvious difference.

Best regards,
Mathias