This is a gentoo problem I hadn't seen before:
Building CXX object qt4/src/CMakeFiles/poppler-qt4.dir/poppler-ps-converter.cc.o
/usr/lib/gcc/x86_64-pc-linux-gnu/4.4.5/../../../../x86_64-pc-linux-gnu/bin/ld: warning: libopenjpeg.so.2, needed by /usr/lib/libpoppler.so.13, not found (try using -rpath or -rpath-link)
/usr/lib/libpoppler.so.13: undefined reference to `opj_set_event_mgr' /usr/lib/libpoppler.so.13: undefined reference to `opj_cio_open'
/usr/lib/libpoppler.so.13: undefined reference to `opj_image_destroy' /usr/lib/libpoppler.so.13: undefined reference to `opj_cio_close'
/usr/lib/libpoppler.so.13: undefined reference to `opj_set_default_decoder_parameters'
/usr/lib/libpoppler.so.13: undefined reference to `opj_destroy_decompress'
/usr/lib/libpoppler.so.13: undefined reference to `opj_create_decompress'
/usr/lib/libpoppler.so.13: undefined reference to `opj_decode'
/usr/lib/libpoppler.so.13: undefined reference to `opj_setup_decoder'
collect2: ld returned 1 exit status linking of temporary binary failed:
Command '['gcc', '-o', '/var/tmp/portage/app-text/poppler-0.16.7/work/poppler-0.16.7_build/glib/tmp-introspectN6cqKw/Poppler-0.16', '-O2', '-march=nocona', '-pipe', '-L.', '-Wl,-rpath=.', '-lpoppler-glib', '-pthread', '-lgio-2.0', '-lgobject-2.0', '-lgmodule-2.0', '-lgthread-2.0', '-lrt', '-lglib-2.0', '/var/tmp/portage/app-text/poppler-0.16.7/work/poppler-0.16.7_build/glib/tmp-introspectN6cqKw/Poppler-0.16.o']' returned non-zero exit status 1
make[2]: *** [glib/Poppler-0.16.gir] Error 1
make[1]: *** [glib/CMakeFiles/gir-girs.dir/all] Error 2
[ 93%] Building CXX object qt4/src/CMakeFiles/poppler-qt4.dir/poppler-qiodeviceoutstream.cc.o
[ 94%] Building CXX object qt4/src/CMakeFiles/poppler-qt4.dir/poppler-sound.cc.o
[ 94%] Building CXX object qt4/src/CMakeFiles/poppler-qt4.dir/poppler-textbox.cc.o
[ 94%] Building CXX object qt4/src/CMakeFiles/poppler-qt4.dir/poppler-page-transition.cc.o
[ 95%] Building CXX object qt4/src/CMakeFiles/poppler-qt4.dir/__/__/poppler/ArthurOutputDev.cc.o
Linking CXX shared library libpoppler-qt4.so
Turns out, I needed to build with "-introspection" in order to build it again with "introspection". Or maybe I could just globally disable introspection, but not sure what that would change, it looks like a Gnome thing. As usual I ended up with lots of Gnome and KDE installed, and really I still just use Enlightenment everywhere. If it wasn't Enlightenment, it would be Windowmaker or something similar.