regcomp.c: Shun ANYOF_NONBITMAP_NON_UTF8

regcomp.c: Shun ANYOF_NONBITMAP_NON_UTF8

As noted in the comments in the code for this commit, this flag has
higher consequences than others when it is inappropriately set in the
synthetic start class.  This patch causes it to not be set unless there
is some path in the regex engine that needs it, but once set it is never
cleared.  This results in a different set of false positives than
currently, but the current set can have this set even if there is no
path in the engine that needs it.