Revert part of rS341838 as it turned out to trigger a subtle issue in less when doing search and there are no matches; I'm not seeing it affecting anything else (AFAIK, and it's strange), but it wasn't directly related to fixing the endless loop, and was done only because I was apparently misunderstanding the relation to the bitmap used in other regcomp parts. In any case, it should have been only modified to use NC_MAX instead of NC, and so this change does.
I wasn't able to come up with any meaningful reproducer except for doing the search in less several times. Other than that, lib/libc/regex, usr.bin/grep, usr.bin/sed all (still) pass.
For the record: while it is good practice to request reviews before committing, IMHO they dont make much sense, and are not required at all, for reverts. After all they stand for things all the initial reviewers missed in the first place ;).