pkg config module does not search default paths when --libs returns -L....
if a pkg config file returns a linker args string with -L in it then cmake will ONLY search along that path. So for example if I have liblcm which links against glib2.0 and I install lcm in /usr/local, cmake will (silently!) produce the wrong output. Not only does it not find glib but it does not even add lcm to the linker command line in this case.
It's not super clear how this should be fixed but imo what happens now is definitely wrong