build-sys: meson: Correctly set up RPATH

This was being done automatically by autotools, now we need to manually
specify this for each executable/library with a dependency in a
non-standard directory.

src/modules/gsettings/meson.build

@@ -11,6 +11,7 @@ gsettings_helper = executable('gsettings-helper',
   link_with : [libpulsecommon, libpulse],
   dependencies : [gio_dep],
   install_dir : pulselibexecdir,
+  install_rpath : privlibdir,
   install : true,
 )