benchfn used to rely on mem.h, and util,
which in turn relied on platform.h.
Using benchfn outside of zstd required to bring all these dependencies.
Now, dependency is reduced to timefn only.
This required to create a separate timefn from util,
and rewrite benchfn and timefn to no longer need mem.h.
Separating timefn from util has a wide effect accross the code base,
as usage of time functions is widespread.
A lot of build scripts had to be updated to also include timefn.
In #1520 it is described that FreeBSD doesn't detect symbolic links. The
same is true for OpenBSD. This diff fixes this issue for OpenBSD. I'm
guessing that something similar works for FreeBSD as well. However, I'm
unable to test this.
Similar to Apple, use the native physical core count sysctl, when available.
This is a little repetitive (it's basically the __APPLE__ method plus the
otherBSD method concatenated together) but seemed clearer than any way that
would totally eliminate repetition.
The __FreeBSD_version check only tests the version of the FreeBSD kernel
that zstd is compiled on; importantly, it may be run on a different version.
So the compile-time check is a little naive and needs to be able to fallback
to work on older versions of FreeBSD. For a similar reason, it may make
sense to simply eliminate the __FreeBSD_version check entirely. The
tradeoff is that a spurious sysctlbyname would be issued when -T0 is used on
older kernels.
