maint: news: announce that Bison 3.6 drops YYERROR_VERBOSE

[Akim Demaille]

commit 961ea2ac8548f8f5e8b48b89e680931ba6c7b15e
Author: Akim Demaille <address@hidden>
Date:   Sat Apr 4 14:52:58 2020 +0200

    news: announce that Bison 3.6 drops YYERROR_VERBOSE
    
    * NEWS: here.

diff --git a/NEWS b/NEWS
index 2de5799e..d5d1d019 100644
--- a/NEWS
+++ b/NEWS
@@ -2,6 +2,18 @@ GNU Bison NEWS
 
 * Noteworthy changes in release ?.? (????-??-??) [?]
 
+** WARNING: Future backward-incompatibilities!
+
+  TL;DR: replace "#define YYERROR_VERBOSE 1" by "%define parse.error verbose".
+
+  Bison 3.6 will no longer support the YYERROR_VERBOSE macro; the parsers
+  that still depend on it will produce Yacc-like error messages (just
+  "syntax error").  It was superseded by the "%error-verbose" directive in
+  Bison 1.875 (2003-01-01).  Bison 2.6 (2012-07-19) clearly announced that
+  support for YYERROR_VERBOSE would be removed.  Note that since Bison 3.0
+  (2013-07-25), "%error-verbose" is deprecated in favor of "%define
+  parse.error verbose".
+
 ** Bug fixes
 
   Fix portability issues of the package itself on old compilers.