I don't think we are currently installing the include files in the nss
package correctly.
We currently place them in $PREFIX/include/nss/nss and install a couple
of other files in $PREFIX/include/nss/dbm.
I think they should go up a level to just $PREFIX/include/nss and not
install the dbm files. That would seem to be consistent with what other
systems do.
At the very least, if we don't want to move them, we should fix
pkgconfig/nss.pc to (also?) specify -I/usr/pkg/include/nss/nss