The easiest way to match the output of either Bison or yacc is with
grep, so introduce a new test helper, check_grep, to facilitate.
I don't know if we've ever made an official decision on this ... but my
feeling has been that requring flex and/or bison is fine. Automake
sets up things so when a distribution is created the C language files
produced by flex and bison are distributed so there is no requirement to
have the GNU variants to build nmh. You would need them to build from
the repository, though.
I realize this is something reasonable people can disagree on, so I am
welcome to hearing what others think about this.
--Ken