yacc: declare yyerror/yylex only when POSIXLY_CORRECT

The recent changes to comply with POSIX are breaking Automake's test
suite.
Reported by Kiyoshi Kanazawa.
<https://lists.gnu.org/r/bug-bison/2021-09/msg00005.html>

To limit the impact of POSIX changes, bind them to $POSIXLY_CORRECT.
Suggested by Karl Berry.
<https://lists.gnu.org/r/bug-bison/2021-09/msg00009.html>

The existing `maintainer-check-posix` Make target checks these
changes.

* src/getargs.h, src/getargs.c (set_yacc): New.
Use it.
* data/skeletons/bison.m4 (b4_posix_if): New.
* data/skeletons/yacc.c (b4_declare_yyerror_and_yylex): Use it.
* doc/bison.texi, tests/local.at: Adjust.

src/getargs.c

@@ -71,6 +71,18 @@ struct bison_language const *language = &valid_languages[0];
 
 typedef int* (xargmatch_fn) (const char *context, const char *arg);
 
+void
+set_yacc (location loc)
+{
+  yacc_loc = loc;
+  if (getenv ("POSIXLY_CORRECT"))
+    muscle_percent_define_insert ("posix",
+                                  loc,
+                                  muscle_keyword, "",
+                                  MUSCLE_PERCENT_DEFINE_D);
+}
+
+
 /** Decode an option's key.
  *
  *  \param opt        option being decoded.
@@ -631,8 +643,7 @@ static struct option const long_options[] =
 };
 
 /* Build a location for the current command line argument. */
-static
-location
+static location
 command_line_location (void)
 {
   location res;
@@ -835,7 +846,7 @@ getargs (int argc, char *argv[])
 
       case 'y':
         warning_argmatch ("yacc", 0, 0);
-        yacc_loc = loc;
+        set_yacc (loc);
         break;
 
       case COLOR_OPTION:

src/getargs.h

@@ -140,6 +140,7 @@ void getargs (int argc, char *argv[]);
 /* Used by parse-gram.y.  */
 void language_argmatch (char const *arg, int prio, location loc);
 void skeleton_arg (const char *arg, int prio, location loc);
+void set_yacc (location loc);
 
 /** In the string \c s, replace all characters \c from by \c to.  */
 void tr (char *s, char from, char to);

src/parse-gram.c

@@ -1,4 +1,4 @@
-/* A Bison parser, made by GNU Bison 3.7.5.297-b46a.  */
+/* A Bison parser, made by GNU Bison 3.8.  */
 
 /* Bison implementation for Yacc-like parsers in C
 
@@ -46,10 +46,10 @@
    USER NAME SPACE" below.  */
 
 /* Identify Bison output, and Bison version.  */
-#define YYBISON 30705
+#define YYBISON 30800
 
 /* Bison version string.  */
-#define YYBISON_VERSION "3.7.5.297-b46a"
+#define YYBISON_VERSION "3.8"
 
 /* Skeleton name.  */
 #define YYSKELETON_NAME "yacc.c"
@@ -3129,7 +3129,7 @@ handle_yacc (location const *loc)
   const char *directive = "%yacc";
   bison_directive (loc, directive);
   if (location_empty (yacc_loc))
-    yacc_loc = *loc;
+    set_yacc (*loc);
   else
     duplicate_directive (directive, yacc_loc, *loc);
 }

src/parse-gram.h

@@ -1,4 +1,4 @@
-/* A Bison parser, made by GNU Bison 3.7.5.297-b46a.  */
+/* A Bison parser, made by GNU Bison 3.8.  */
 
 /* Bison interface for Yacc-like parsers in C
 
@@ -215,6 +215,7 @@ struct GRAM_LTYPE
 
 
 
+
 int gram_parse (void);
 
 /* "%code provides" blocks.  */

src/parse-gram.y

@@ -1112,7 +1112,7 @@ handle_yacc (location const *loc)
   const char *directive = "%yacc";
   bison_directive (loc, directive);
   if (location_empty (yacc_loc))
-    yacc_loc = *loc;
+    set_yacc (*loc);
   else
     duplicate_directive (directive, yacc_loc, *loc);
 }