I found the reason pango is broken (for me at least).  There are two
versions of fontconfig.pc on my machine:  one installed by the
fontconfig package in /usr/pkg/lib/pkgconfig/ and the other one
is installed by XFree in /usr/X11R6/lib/pkgconfig/

The source of the second one is here:
/usr/xsrc/xfree/xc/lib/fontconfig/fontconfig.pc and this is
the one that the pango package was using without success to
link libfontconfig.

#cat fontconfig.pc
prefix=/usr/X11R6
exec_prefix=/usr/X11R6/bin
libdir=/usr/X11R6/lib
includedir=/usr/X11R6/include

Name: Fontconfig
Description: Font configuration and customization library
Version: 1.0.1
Libs: -Wl,-R${libdir} -L${libdir} -lfontconfig
Cflags: -I${includedir}

The question is why ld coundn't find libfontconfig which
is right in /usr/X11R6/lib where it's supposed to be.

Anyway, I moved the fontconfig.pc file out of the way and
pango proceeded to use (and find) the library in /usr/pkg/lib.

Is there any reason to keep the fontconfig package installed
on a machine with the native XFree fontconfig libraries?

Looks like Xft and freetype are also duplicated, and probably
others I haven't noticed.