[CMake] How to query compiler definitions?

[SF Markus Elfring]

> Why don't you include the check for NDEBUG in in your "debug-sources"?

This is the case already.


> The time you'll waste compiling these files will be negligible, and it
> would work with mult-config IDE's.

I find this view debatable. I would appreciate if I can express in the build 
specification that a few source file are optional for the compilation because of 
this well-known preprocessor symbol.

Regards,
Markus