11193 cmn_err.9f: UNSUPP: unsupported escape sequences
This is required for mandoc 1.14.5 update (#11190).

Before:
$ mandoc -Tlint -Wwarning ~/ws/illumos-gate/usr/src/man/man9f/cmn_err.9f 
mandoc: /export/home/newman/ws/illumos-gate/usr/src/man/man9f/cmn_err.9f:191:8: UNSUPP: unsupported escape sequence: \!
mandoc: /export/home/newman/ws/illumos-gate/usr/src/man/man9f/cmn_err.9f:195:8: UNSUPP: unsupported escape sequence: \?
mandoc: /export/home/newman/ws/illumos-gate/usr/src/man/man9f/cmn_err.9f:205:8: UNSUPP: unsupported escape sequence: \?
mandoc: /export/home/newman/ws/illumos-gate/usr/src/man/man9f/cmn_err.9f:356:8: UNSUPP: unsupported escape sequence: \?


After:
$ mandoc -Tlint -Wwarning /usr/share/man/man9f/cmn_err.9f 

$ mandoc -l /usr/share/man/man9f/cmn_err.9f

     !       The message goes only to the system log.
     ...
     ?       If level is also CE_CONT, the message is always sent to the
     ...
     condition is met, the "?" character has no effect and is simply
     ...
     Because of the leading "?" character in the format string, this