Thus it ought to be possible, though I have not yet tried it.
You have a file, something like: load.h
You need to include it multiple times, compiled with different flags.
So - it's never going to be in load.cxx or whatever that's called.
Here is an example: https://github.com/google/gemma.cpp/blob/9dfe2a76be63bcfe679...
Let's stop here, it doesn't seem like we understand each other.
Thus it ought to be possible, though I have not yet tried it.