C++: let %require "3.2" disable the generation of obsolete files

The files stack.hh and position.hh are deprecated.  Rather than
devoting specify %define variables to discard them (api.position.file
and api.stack.file), and rather than having to use special rules when
api.location.file is used, let's simply decide that from %require
"3.2" onwards, these files will not be generated.

The only noticeable thing here is that, in order to be able to check
the behavior of %require "3.2", to have this version (which is still
3.1-*) to accept %require "3.2".

* src/gram.h, src/gram.c (required_version): New.
* src/parse-gram.y (version_check): Set it.
* src/output.c (prepare): Pass it m4.
* data/bison.m4 (b4_required_version_if): Receive it and use it.
* data/location.cc, data/stack.hh: Replace the api.*.file with only
required version comparison.
* tests/input.at: No longer check api.stack.file and api.position.file.
* NEWS, doc/bison.texi: Don't mention them.
Document the %require 3.2 behavior.
* tests/output.at: Use %require 3.2 instead.

doc/bison.texi

@@ -4788,6 +4788,14 @@ status 63).
 %require "@var{version}"
 @end example
 
+Some deprecated behaviors are disabled for some required @var{version}:
+@table @code
+@item "3.2"
+The C++ deprecated files @file{position.hh} and @file{stack.hh} are no
+longer generated.
+@end table
+
+
 @node Token Decl
 @subsection Token Type Names
 @cindex declaring token type names
@@ -5834,9 +5842,6 @@ in @var{file}.  This file name can be relative (to where the parser file is
 output) or absolute.
 @end table
 
-Defining it implies @samp{%define api.position.file none} and @samp{%define
-api.stack.file none}.
-
 @item Default Value:
 Not applicable if locations are not enabled, or if a user location type is
 specified (see @code{api.location.type}).  Otherwise, Bison's
@@ -5893,28 +5898,6 @@ Introduced in Bison 2.7 for C, C++ and Java.  Introduced under the name
 @end itemize
 @end deffn
 
-@c ================================================== api.position.file
-@deffn {Directive} {%define api.position.file} @code{none}
-
-@itemize @bullet
-@item Language(s): C++
-
-@item Purpose:
-Disable the generation of the legacy file @file{position.hh}.  The class
-@code{position} is now defined where the class @code{location} is.
-
-@item Accepted Values: @code{none}
-
-@item Default Value:
-@code{none} if @code{api.location.file} is defined, otherwise a useless
-@file{position.hh} is generated for backward compatibility.
-
-@item History:
-Introduced in Bison 3.2.
-@end itemize
-@end deffn
-
-
 @c ================================================== api.prefix
 @deffn {Directive} {%define api.prefix} @{@var{prefix}@}
 
@@ -6001,27 +5984,6 @@ the @code{full} value was introduced in Bison 2.7
 
 
 
-@c ================================================== api.stack.file
-@deffn {Directive} {%define api.stack.file} @code{none}
-
-@itemize @bullet
-@item Language(s): C++
-
-@item Purpose:
-Disable the generation of the legacy file @file{stack.hh}.
-
-@item Accepted Values: @code{none}
-
-@item Default Value:
-@code{none} if @code{api.location.file} is defined, otherwise a useless
-@file{stack.hh} is generated for backward compatibility.
-
-@item History:
-Introduced in Bison 3.2.
-@end itemize
-@end deffn
-
-
 @c ================================================== api.token.constructor
 @deffn Directive {%define api.token.constructor}
 
@@ -10681,12 +10643,9 @@ extension of these two files follow the same rules as with regular C parsers
 (@pxref{Invocation}).
 
 @item position.hh
-A useless legacy file.  To get rid of it, use @samp{%define api.stack.file
-none}, or define @code{api.location.file}.
-
-@item stack.hh
-A useless legacy file.  To get rid of it, use @samp{%define
-api.position.file none}, or define @code{api.location.file}.
+@itemx stack.hh
+Useless legacy files.  To get rid of then, use @samp{%require "3.2"} or
+newer.
 @end table
 
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