Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

This reverts commit b590a13f.

Should close #5571

If we don't build pkg-config (because a previous installation exists
somewhere else), autoconf won't find PKG_* m4 macros and fail to
run on packages using them (if they don't ship the macros either)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

This saves a whole lot of float conversion and simplifies the code.

Only 1 second interval has ever been used.

One last full rebuild for this!

The implementation was slow/inefficient. This is really silly for
_performance_ counters. And contrary to the other statistics, nothing
actually reads them, except for debug logs.

If you really want debug-only performance timers, use this:

    mtime_t start, end;

    start = mdate();
    compute_decimals_of_Pi(100);
    end = mdate();
    msg_Dbg(obj, "spent %"PRIu64" us computing", end - start);

So that the user notices it when it doesn't work
Ref #5569
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

Atoms mvex, mehd, trex and sdtp are found at least in PIFF (isml) files.
This a first step towards Smooth Streaming support in VLC.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

And reorder alphabetically, so such mistakes don't happen again

Do not leak -lncursesw in LIBS

only error out if asked with --enable-skins2

split out open box function

Use our own check which also recognizes static inline functions

Don't use ac_cv_search cached value because it could contain
"no" or "none required" which aren't valid link flags

AC_CHECK_LIB(main, xxx) did not exactly search for main symbol, it
searched for the presence of the library.
Instead we look for a required symbol.

We don't use e.g. pthread_mutex_lock because some pthread symbols
are available in glibc, but not all.

Not finding pthread library is not an error, because at least OS/2 and
symbian don't need it. (We skip the check on Windows already)