With texinfo 5.1, XEmacs 21.4.22 fails to build custom.info from
custom.texi:

cd
/var/tmp/portage/app-editors/xemacs-21.4.22-r2/work/xemacs-21.4.22/man
&& make  info
make[1]: Entering directory
`/var/tmp/portage/app-editors/xemacs-21.4.22-r2/work/xemacs-21.4.22/man'
makeinfo -o ../info/cl.info cl.texi
makeinfo -o ../info/custom.info custom.texi
custom.texi:63: raising the section level of @section which is too low
make[1]: *** [../info/custom.info] Error 1
make[1]: Leaving directory
`/var/tmp/portage/app-editors/xemacs-21.4.22-r2/work/xemacs-21.4.22/man'
make: *** [info] Error 2

(XEmacs 21.5.33 builds just fine.)