Problem building fontconfig w/ read-only /usr/ports

[Cory Bajus]

Marcus,

A recent change to x11-fonts/fontconfig prevents this port
from building if /usr/ports is mounted read-only.  Here
is the error message that I receive when attempting to
build this port:

 install -c -o root -g wheel -m 444 ./fontconfig.pc /usr/X11R6/libdata/pkgconfig
/fontconfig.pc
gmake[2]: Leaving directory `/usr/work/usr/ports/x11-fonts/fontconfig/work/fontc
onfig-2.1.92'
gmake[1]: Leaving directory `/usr/work/usr/ports/x11-fonts/fontconfig/work/fontc
onfig-2.1.92'
===>   Generating temporary packing list
cannot create /usr/ports/x11-fonts/fontconfig/pkg-install: read-only file system
*** Error code 2
Stop in /usr/ports/x11-fonts/fontconfig.
*** Error code 1

The problem seems to be cause by this entry in the post-install
section of the Makefile:

@${SED} -e 's|%%PREFIX%%|${PREFIX}|' < ${FILESDIR}/pkg-install.in \
> ${PKGINSTALL}

This is attempting to write to a file named pkg-install in
/usr/ports/x11-fonts/fontconfig.  Is it possible to write
this file to ${WRKDIR} instead?  I have WRKDIRPREFIX set to
a writeable directory.

Please let me know if you need any more information about my
configuration.

Thanks in advance,

Cory.