New review comment by sgn on void-packages repository

https://github.com/void-linux/void-packages/pull/31706#discussion_r660218263

Comment:
- We don't want the flags KitWare implies (`-DNDEBUG`)
- racer wants their `-O3`
- We allow build without debug, too (`unset XBPS_DEBUG_PKGS`). And sometime, `-g` is unmanagable, look at `llvm12` ;)
- broken build systems are broken build systems, to them, there are only `Debug` and `Release`