audio/ardour6: Update to 6.9.0
Fix MP3 audio export. It was unavailable due to missing ffmpeg_harvid and
ffprobe_harvid in $PATH.
Add dependencies on harfbuzz and fftw3 libraries, which were implicitly linked.
While here, pet linters.
Reported by: firstname.lastname@example.org
audio/ardour6: fix build on GCC architectures
Undefine _POSIX_SOURCE to make macros in errno.h available:
error: 'EAFNOSUPPORT' was not declared in this scope
42 | address_family_not_supported = EAFNOSUPPORT,
error: 'EADDRINUSE' was not declared in this scope
43 | address_in_use = EADDRINUSE,
Also tested to build with Clang.
MFH: 2020Q4 (fix build blanket)