How to force port respecting PKGCONFIGDIR?

[O. Hartmann]

Hello.
As I realized while trying to port xerces-c version 3.1.1 in an test 
environment as suggested in the porters handbook, the software, which is 
capable of using the GNU autotoll environment, installs its xerces-c.pc 
file into ${PREFIX}/lib/pkgconfig/ and not according the
FreeBSD paradigm into  ${PREFIX}/libdata/pkgconfig/. I see three ports 
having already installed their obviously mislead *.pc file into 
${PREFIX}/lib/pkgconfig/ in real-world-installations (libvlc.pc, 
lapackpp.pc and vlc-plugin.pc) on all of my FreeBSD boxes where these 
packages are installed - every other package using pkg-config seems to 
have their config files installed at the proper place and therefor 
${PREFIX}/libdata/pkgconfig/ is well populated.

The question is: how can I trim my port's Makefile to accept and respect 
FreeBSD's path? I tried to figure out what directive has to be set and 
passed to any kind of environemnt, but the handbook silence this out. I 
have a faint clue that all directives tagged *_PC_* has to do something 
with this, but in ports I examined which install their pkg-config files 
in the proper way I did not find any hint.

Please set me CC if responding due to I'm not subscriber of the list.

Thanks.

Oliver