Broken package config paths on macOS in 1.20.0 release

See for example gstreamer-base-1.0.pc.

In GStreamer 1.18.5 it looks like this:

prefix=/Library/Frameworks/GStreamer.framework/Versions/1.0
exec_prefix=${prefix}
libdir=${prefix}/lib
includedir=${prefix}/include/gstreamer-1.0
datarootdir=${prefix}/share
datadir=${datarootdir}
girdir=${datadir}/gir-1.0
typelibdir=${libdir}/girepository-1.0

Name: GStreamer base classes
Description: Base classes for GStreamer elements
Requires: gstreamer-1.0
Version: 1.18.5
Libs: -L${libdir} -lgstbase-1.0
Cflags: -I${includedir}

In GStreamer 1.20.0 it contains the private looking path /Users/matt/Projects/cerbero/build/dist/darwin_universal which most likely doesn't exist on any system consuming the library:

prefix=/Users/matt/Projects/cerbero/build/dist/darwin_universal
libdir=${prefix}/lib
includedir=${prefix}/include

exec_prefix=${prefix}
toolsdir=${exec_prefix}/bin
pluginsdir=${libdir}/gstreamer-1.0
datarootdir=${prefix}/share
datadir=${datarootdir}
girdir=${datadir}/gir-1.0
typelibdir=${libdir}/girepository-1.0
libexecdir=${prefix}/libexec
pluginscannerdir=${libexecdir}/gstreamer-1.0

Name: gstreamer-base-1.0
Description: Base classes for GStreamer elements
Version: 1.20.0
Requires: gstreamer-1.0
Requires.private: gobject-2.0, glib-2.0 >= 2.56.0, gmodule-2.0
Libs: -L${libdir} -lgstbase-1.0
Cflags: -I${includedir}/gstreamer-1.0

This breaks my buildscript which was depending on the common install path to fix both include dirs and handle @rpath correctly. It's probably also the cause for issue #362 (closed), though I didn't confirm that.