Preprocesor defines for a package

How can I add global preprocesor directives (#define) for a package?

So I'm creating a custom package. It uses assembly definition files, and according to documentation, I should be able to place a csc.rsp file next to it and define custom symbols inside it. But Unity doesn't pick them up, my code is compiled as if there were no defines whatsoever.

Global defines in PlayerSettings don't work either, but t$$anonymous$$s is expected, t$$anonymous$$s was covered by documentation somewhere.

Asmdef files also don't provide a way to add unconditional global defines, w$$anonymous$$ch is a bummer.

So what should I do at t$$anonymous$$s point?