build: Support the meson build system

Meson is on track to replace autotools as the build system of choice,
so support it in addition to autotools. If all goes well, we'll
eventually be able to drop the latter ...

https://bugzilla.gnome.org/show_bug.cgi?id=783229

js/misc/meson.build

@@ -0,0 +1,16 @@
+jsconf = configuration_data()
+jsconf.set('PACKAGE_NAME', meson.project_name())
+jsconf.set('PACKAGE_VERSION', meson.project_version())
+jsconf.set('GETTEXT_PACKAGE', meson.project_name())
+jsconf.set('LIBMUTTER_API_VERSION', mutter_api_version)
+jsconf.set10('HAVE_BLUETOOTH', bt_dep.found())
+jsconf.set10('HAVE_NETWORKMANAGER', have_networkmanager)
+jsconf.set('datadir', datadir)
+jsconf.set('libexecdir', libexecdir)
+jsconf.set('sysconfdir', sysconfdir)
+
+config_js = configure_file(
+  input: 'config.js.in',
+  output: 'config.js',
+  configuration: jsconf
+)