meson: Add udev_dir option

Same as in gnome-settings-daemon, allows overriding where to install
udev rules files.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1844>

data/meson.build

@@ -61,6 +61,6 @@ install_data(['mutter-schemas.convert'],
 
 if have_libgudev
   install_data(['61-mutter.rules'],
-    install_dir: join_paths(udevdir, 'rules.d'),
+    install_dir: join_paths(udev_dir, 'rules.d'),
   )
 endif

meson.build

@@ -181,7 +181,11 @@ if have_libgudev
   libudev_dep = dependency('libudev', version: udev_req)
   gudev_dep = dependency('gudev-1.0', version: gudev_req)
   udev_dep = dependency('udev')
-  udevdir = udev_dep.get_pkgconfig_variable('udevdir')
+
+  udev_dir = get_option('udev_dir')
+  if udev_dir == ''
+    udev_dir = udev_dep.get_pkgconfig_variable('udevdir')
+  endif
 endif
 
 have_native_backend = get_option('native_backend')

meson_options.txt

@@ -69,6 +69,12 @@ option('udev',
   description: 'Enable udev support when using the X11 backend'
 )
 
+option('udev_dir',
+  type: 'string',
+  value: '',
+  description: 'Absolute path of the udev base directory'
+)
+
 option('libwacom',
   type: 'boolean',
   value: true,