Compilation issue: `jitterentropy.c` fails to build when optimisation is set in `CFLAGS`.

[dreirund]

I created an Arch Linux AUR package robrix-git (↗ build recipe) and built it.

Upon doing so, I encountered that I had to pass -O0 to the $CFLAGS, otherwise compilation would abort when trying to compile jitterentropy.c:

  cargo:warning=   47 |  #error "The CPU Jitter random number generator must not be compiled with optimizations. See documentation. Use the compiler switch -O0 for compiling jitterentropy.c."

By default, I have -O3 in the $CFLAGS to create optimised code. Where I now have passed -O0, this applies to all C sources which get compiled by the cargo build run.
Can you make that -O0 is explicitly passed by your build system to the sources that need it, so that the rest can still use optimisation?

Regards!