udev: Make Udev optional

In order to further simplify "unprivileged" builds, add "udev" boolean,
which make installing Udev rules optional.

I.e. without requiring any ugly hacks (mktemp -d), an privileged build
capable of running PulseAudio and JACK applications, can be configured
trivially:

meson --prefix=~/.local build
meson configure build -Dsystemd-user-unit-dir=$HOME/.config/systemd/user
meson configure build -Dpipewire-alsa=false
meson configure build -Dudev=false

Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@iki.fi>

meson_options.txt

@@ -137,6 +137,10 @@ option('pw-cat',
        description: 'Build pw-cat/pw-play/pw-record',
        type: 'boolean',
        value: true)
+option('udev',
+       description: 'Enable Udev integration',
+       type: 'boolean',
+       value: true)
 option('udevrulesdir',
        type : 'string',
        description : 'Directory for udev rules (defaults to /lib/udev/rules.d)')

spa/plugins/alsa/meson.build

@@ -42,7 +42,7 @@ executable('test-timer',
   install : false,
 )
 
-if libudev_dep.found()
+if get_option('udev') and libudev_dep.found()
   install_data(alsa_udevrules,
     install_dir : udevrulesdir,
   )