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?