libopenmpt: update to 0.5.9.

### libopenmpt 0.5.9 (2021-05-16)

*  `Makefile` `CONFIG=emscripten` does not pass linker options to the compiler
    any more, which caused latest Emscripten to issue warnings.

*  The retrigger effect didn't work correctly for OPL instruments in some cases
    depending on the chosen output sample rate.
*  S3M: Emulate IT short sample retrigger quirk in S3M files saved with
    Impulse Tracker and Schism Tracker.
*  ProTracker 3.6 doesn't support sample swapping. It is now disabled when
    loading a ProTracker 3.6 IFF module.
*  Some files with "hidden" garbage patterns were not played correctly since
    libopenmpt 0.5.3.
*  MOD: E9x retrigger now works the same way as in ProTracker 2.
*  MDL: Improve auto-vibrato accuracy.
*  669: Reject files that contain any pattern tempo higher than 15.
*  Reduce memory consumption of malformed XPK-compressed files.

*  mpg123: Update to v1.27.2 (2021-05-08).

(fcambus)