Fix setting audacity_use_midi=off

When disabling MIDI support, cmake will fail:

```
$ cmake -B build -Daudacity_use_midi=off
[...]
CMake Error at cmake-proxies/CMakeLists.txt:314 (message):
  EXPERIMENTAL_MIDI_OUT requires USE_MIDI
```

Disable `EXPERIMENTAL_MIDI_OUT` in case MIDI support was explicitly
disabled.

Forwarded: https://github.com/audacity/audacity/pull/3717
Signed-off-by: Benjamin Drung <benjamin.drung@canonical.com>
Gbp-Pq: Name Fix-setting-audacity_use_midi-off.patch

Fix rpath for private libraries on Linux

Installing audacity on Linux will produce private libraries that have
`RUNPATH` set to the build directory instead of the installation
directory.

The root cause is that the library directory is copied to the
installation directory without touching the libraries. The cmake wiki
says in RPATH handling caveats [1]: "Since install-side RPATH tweaking
is an operation that is done by target-specific installation handling,
any target that should have its install RPATH changed (e.g. to
`CMAKE_INSTALL_RPATH`) needs to end up in the installation via an
`install(TARGETS ...)` signature and not via directory-based copying."

So replace `install(DIRECTORY ...)` by individual `install(TARGETS ...)`
for the libraries and modules. Then cmake will replace the `RUNPATH` to
`$ORIGIN/../lib/audacity`, which is still incorrect. Therefore set
`INSTALL_RPATH` explicitly.

Fixes: https://github.com/audacity/audacity/issues/3289
Forwarded: https://github.com/audacity/audacity/pull/3671
[1] https://gitlab.kitware.com/cmake/community/-/wikis/doc/cmake/RPATH-handling#caveats
Signed-off-by: Benjamin Drung <benjamin.drung@canonical.com>
Gbp-Pq: Name Fix-rpath-for-private-libraries-on-Linux.patch

audacity (3.6.4+dfsg-1) unstable; urgency=medium

  * New upstream version 3.6.4+dfsg

[dgit import unpatched audacity 3.6.4+dfsg-1]

Import audacity_3.6.4+dfsg.orig.tar.xz

[dgit import orig audacity_3.6.4+dfsg.orig.tar.xz]

Import audacity_3.6.4+dfsg-1.debian.tar.xz

[dgit import tarball audacity 3.6.4+dfsg-1 audacity_3.6.4+dfsg-1.debian.tar.xz]