since only UTIL_DISPLAY() depended on it.

from *.h to *.c
so that they don't get transitively included
into users of util.h.

complaining about a `const` property on one side but not the other.

shows that the resulting object just takes ownership of provided buffer.

protecting "/dev/null" from having its permissions changed.

also : minor : improved consistency of util.h API

free() is compatible with NULL,
let's free() unconditionnally

pass basic tests

New flag to specify output directory destination for multiple files.

adding support for -O flag: multiple files into one directory for compressions (decompression to come)

utime is deprecated by POSIX 2008 and optionally not available with
uClibc-ng.

Got rid of a few useless headers in timefn.h.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

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.

generated redefinitions

better error message
with test