I missed installing the xorg-x11-fonts-ISO8859-1-{75,100}dpi packages when upgrading a whole bunch of packages to devel. After that, emacs couldn't start because it couldn't find its fonts. Apparently it has default X resources requireing fonts that are in those packages. Either it needs to have different default fonts (perhaps just remove the iso8859-1 part from the resources and let it get whichever it can find), or it needs to depend on those font packages.
*** This bug has been marked as a duplicate of 174614 ***