[CMake] CHECK_C_SOURCE_COMPILES and include_directories

[Florian Weimer]

* Rolf Eike Beer:

> Florian Weimer wrote:
>
>> Is there a way to make CHECK_C_SOURCE_COMPILES honor the discovered
>> include directories?
>
>  cmake --help-module CheckCSourceCompiles
>
> The following variables may be set before calling this macro to modify
> the way the check is run:
> […]
>  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?