Add support for nios2

When compiling jack on nios2, compilation fails because NGREGS is not
defined. Since this is only for debug output on segmentation faults, stub
the debug print out like it's been done for other platforms before.

Inspired by
https://github.com/jackaudio/jack2/commit/d11bb095291d8880508c87adfe625bf2bcab1456



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>

allow to use source date for man page generation

This reverts commit b4e7e875.

this enables making reproducible builds of this package

Fix Netjack crashes due to broken alignment

See discussion at http://comments.gmane.org/gmane.comp.audio.jackit/29516

Use ARM neon intrinsics for AudioBufferMixdown

Correct JackDriver::Open : call to fGraphManager->SetBufferSize has to use current fEngineControl->fBufferSize value.

Correct midiseq.c : better use jack_midi_reset_buffer instead of jack_midi_clear_buffer for output port.

This makes sure header checks work when the third party package is
installed in a non-standard location, as long as a pkg-config file is
found.

It is already defined by conf.define().

Release audio devices when alsa_driver_new fails