[CMake] CHECK_C_SOURCE_COMPILES and include_directories

[Florian Weimer]

* Rolf Eike Beer:

>> >  CMAKE_REQUIRED_INCLUDES = list of include directories
>> 
>> I saw that, but I thought this happens behind the scenes.  Do I have
>> to set this variable in addition to the include_directories directive?
>
> Yes, include_directories() only affects target, i.e. add_executable
> and friends, but not macros like CHECK_C_SOURCE_COMPILES. Those will
> explicitely look at those variables.

Thanks, this does indeed.

(I'm not sure if my initial confusion is specific to me, or if the
documentation could be improved.  But I don't really see where to put
this information so that it is easily discovered.)