No need to redefine DT_PROCNUM and DT_BIND_NOW here, these are provided by MI
<elf_abi.h>.
Cleanup with respect to bad macro arguments.
* Fix .Sm with invalid arg: move arg out and toggle mode.
* Promote "unknown standard" from WARNING to ERROR, it loses information.
* Delete MANDOCERR_BADWIDTH, it would only indicate a mandoc(1) bug.
* Do not report MANDOCERR_BL_LATETYPE when there is no type at all.
* Mention macro names, arguments and fallbacks.