Remove explicit -lm and -db in pkg-config files

elf-NEEDED sections of libjack.so and libjackserver.so should be enough
at link time

libjack/metadata.c: When disabled, make implementations fail with -1,…

… so to mimic jack2 behaviour

This fixes the build with --db=no or when libdb is not installed system-wide

Merge branch 'main' into ladi-1.126

Merge branch 'ladi-1.126-external-jackdbus' into 'ladi-1.126'

wscript: fix use with python2

Use the LADI README

(cherry picked from commit 79fabb4)

Remove jack.spec.in

distro specific receipes belong to downstream packaging repos

(cherry picked from commit dcfb014)

wscript: install jack headers

remove dirs after switch to tools and examples from LADI/jack-tools