When emerging openbox 2.1.2 it fails with the following error message: 

make[3]: Entering directory `/var/tmp/portage/openbox-2.1.2/work/openbox-2.1.2/util'
c++ -DHAVE_CONFIG_H -I. -I. -I.. -DNDEBUG -march=pentium3 -O3 -pipe -fomit-frame-pointer -fforce-addr -falign-functions=4 -fprefetch-loop-arrays -I/usr/X11R6/include -Wall -W -c xftlsfonts.cc
xftlsfonts.cc: In function `int main(int, char**)':
xftlsfonts.cc:101: `XftValueList' undeclared (first use this function)
xftlsfonts.cc:101: (Each undeclared identifier is reported only once for each 
 function it appears in.)
xftlsfonts.cc:101: `vallist' undeclared (first use this function)
make[3]: *** [xftlsfonts.o] Error 1
make[3]: Leaving directory `/var/tmp/portage/openbox-2.1.2/work/openbox-2.1.2/util'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/var/tmp/portage/openbox-2.1.2/work/openbox-2.1.2/util'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/var/tmp/portage/openbox-2.1.2/work/openbox-2.1.2'
make: *** [all-recursive-am] Error 2
!!! ERROR: The ebuild did not complete successfully.
!!! Function commonbox_src_compile, Line -6796, Exitcode 2
!!! (no error message)

I had no problem installing it with xfree 4.2.0 and openbox 2.1.2
When upgrading to xfree 4.2.1, openbox still works although there are no anti-aliased fonts anymore. Remerging openbox fails with te above error.

Michi
Just confirmed here: make[3]: Entering directory `/var/tmp/portage/openbox-2.2.0/work/openbox-2.2.0/util' c++ -DHAVE_CONFIG_H -I. -I. -I.. -DNDEBUG -mcpu=i686 -O3 -pipe -I/usr/X11R6/include -Wall -W -c xftlsfonts.cc xftlsfonts.cc: In function `int main(int, char **)': xftlsfonts.cc:101: `XftValueList' undeclared (first use this function) xftlsfonts.cc:101: (Each undeclared identifier is reported only once xftlsfonts.cc:101: for each function it appears in.) xftlsfonts.cc:101: `vallist' undeclared (first use this function) xftlsfonts.cc:139: warning: enumeration value `FcTypeCharSet' not handled in switch xftlsfonts.cc:139: warning: enumeration value `FcTypeFTFace' not handled in switch xftlsfonts.cc:139: warning: enumeration value `FcTypeLangSet' not handled in switch make[3]: *** [xftlsfonts.o] Error 1 make[3]: Leaving directory `/var/tmp/portage/openbox-2.2.0/work/openbox-2.2.0/util' make[2]: *** [all-recursive] Error 1 make[2]: Leaving directory `/var/tmp/portage/openbox-2.2.0/work/openbox-2.2.0/util' make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory `/var/tmp/portage/openbox-2.2.0/work/openbox-2.2.0' make: *** [all-recursive-am] Error 2 I'll see what more (wood|work)block has to say about it.
Also, I guess you can tell I'm working with 2.2.0, but I get the same thing with 2.1.2.
Created attachment 4993 [details] openbox log with X 4.2.1
openbox 2.1.2 and 2.2.0 both now install with xfree 4.2.1.