Log Message:
bison: update to 3.7.6.

* Noteworthy changes in release 3.7.6 (2021-03-08) [stable]

** Bug fixes

*** Reused Push Parsers

  When a push-parser state structure is used for multiple parses, it was
  possible for some state to leak from one run into the following one.

*** Fix Table Generation

  In some very rare conditions, when there are many useless tokens, it was
  possible to generate incorrect parsers.