configure accepts bison that’s too old for make check-grammar

[nagisa]

Bison 2.7 is too old to compile our src/grammar and doesn’t understand some CLI options we pass to it. Should find out what’s the lowest version of bison that supports our grammar files and check for that.

[alexcrichton]

cc #15880

[steveklabnik]

Triage: almost all of this is either gone or being handled by the new grammar WG, so I'm going to close.