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/echo-cancel/meson.build

@@ -17,5 +17,6 @@ libwebrtc_util = shared_library('webrtc-util',
   dependencies : [libpulse_dep, libpulsecommon_dep, libpulsecore_dep, webrtc_dep],
   link_args : [nodelete_link_args, '-Wl,--unresolved-symbols=ignore-in-object-files'],
   install : true,
+  install_rpath : privlibdir,
   install_dir : modlibexecdir,
 )