1. The logging flags were being ignored (-v, -d)
2. Adds a `--loglevel` argument. Useful when using the debug build for
ASAN/UBSAN to hide extremely noisy debug messages.
This compiles to the same assembly as before even without optimizations and avoids UB.
https://godbolt.org/z/4G5edM
While the UB here is benign, this improves signal-to-noise ratio of UBSAN errors.
Fixes#14005
1. postproc now looks for postprocess.h (there is no postproc.h header).
2. pkg-config fallback condition now works (find_path/library set the
variable to ${var}-NOTFOUND but it was checking for an empty string).