Quoting Helmut Grohne <helmut@subdivi.de>:
Please use arm-linux-gnueabi-pkg-config.
Thanks, that's indeed the correct way! (In my case ${CROSS_COMPILE}pkg-config.) This brings me to the next problem: When installing libglib2.0-dev:armel, libglib2.0-dev gets uninstalled, same for libglib2.0-dev:armhf. That's probably #648621/#683593, right?