Log Message:
bison: update to 3.7.4.

* Noteworthy changes in release 3.7.4 (2020-11-14) [stable]

** Bug fixes

*** Bug fixes in yacc.c

  In Yacc mode, all the tokens are defined twice: once as an enum, and then
  as a macro.  YYEMPTY was missing its macro.

*** Bug fixes in lalr1.cc

  The lalr1.cc skeleton used to emit internal assertions (using YY_ASSERT)
  even when the `parse.assert` %define variable is not enabled.  It no
  longer does.

  The private internal macro YY_ASSERT now obeys the `api.prefix` %define
  variable.

  When there is a very large number of tokens, some assertions could be long
  enough to hit arbitrary limits in Visual C++.  They have been rewritten to
  work around this limitation.

** Changes

  The YYBISON macro in generated "regular C parsers" (from the \ 
"yacc.c"
  skeleton) used to be defined to 1.  It is now defined to the version of
  Bison as an integer (e.g., 30704 for version 3.7.4).