warnings, manywarnings: Assume autoconf >= 2.64

[Bruno Haible]

Gnulib assumes autoconf >= 2.64 since August 2000.
Autoconf 2.64 added the macro AS_VAR_APPEND [1].
Thus, the gl_AS_VAR_APPEND macro, that is an alias of AS_VAR_APPEND, is
no longer needed.

Other packages than gnulib don't use this macro. [2]

Therefore I'm applying this simplification.

[1] https://git.savannah.gnu.org/gitweb/?p=autoconf.git;a=blob;f=NEWS#l960
[2] 
https://codesearch.debian.net/search?q=gl_AS_VAR_APPEND+-path%3A%2Fwarnings.m4+-path%3A%2Fmanywarnings.m4&literal=1


2023-05-28  Bruno Haible  <bruno@clisp.org>

        warnings, manywarnings: Assume autoconf >= 2.64.
        * m4/warnings.m4 (gl_AS_VAR_APPEND): Remove macro.
        (gl_COMPILER_OPTION_IF, gl_WARN_ADD): Use AS_VAR_APPEND instead of
        gl_AS_VAR_APPEND.
        * m4/manywarnings.m4: Likewise.

diff --git a/m4/manywarnings.m4 b/m4/manywarnings.m4
index 7792b4f3b4..a06f26f672 100644
--- a/m4/manywarnings.m4
+++ b/m4/manywarnings.m4
@@ -1,4 +1,4 @@
-# manywarnings.m4 serial 23
+# manywarnings.m4 serial 24
 dnl Copyright (C) 2008-2023 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -6,6 +6,8 @@
 
 dnl From Simon Josefsson
 
+AC_PREREQ([2.64])
+
 # gl_MANYWARN_COMPLEMENT(OUTVAR, LISTVAR, REMOVEVAR)
 # --------------------------------------------------
 # Copy LISTVAR to OUTVAR except for the entries in REMOVEVAR.
@@ -21,7 +23,7 @@ AC_DEFUN([gl_MANYWARN_COMPLEMENT]
       *" $gl_warn_item "*)
         ;;
       *)
-        gl_AS_VAR_APPEND([gl_warn_set], [" $gl_warn_item"])
+        AS_VAR_APPEND([gl_warn_set], [" $gl_warn_item"])
         ;;
     esac
   done
@@ -148,51 +150,51 @@ AC_DEFUN([gl_MANYWARN_ALL_GCC(C
     -Wwrite-strings \
     \
     ; do
-    gl_AS_VAR_APPEND([$1], [" $gl_manywarn_item"])
+    AS_VAR_APPEND([$1], [" $gl_manywarn_item"])
   done
 
   # gcc --help=warnings outputs an unusual form for these options; list
   # them here so that the above 'comm' command doesn't report a false match.
-  gl_AS_VAR_APPEND([$1], [' -Warray-bounds=2'])
-  gl_AS_VAR_APPEND([$1], [' -Wattribute-alias=2'])
-  gl_AS_VAR_APPEND([$1], [' -Wbidi-chars=any,ucn'])
-  gl_AS_VAR_APPEND([$1], [' -Wformat-overflow=2'])
-  gl_AS_VAR_APPEND([$1], [' -Wformat=2'])
-  gl_AS_VAR_APPEND([$1], [' -Wformat-truncation=2'])
-  gl_AS_VAR_APPEND([$1], [' -Wimplicit-fallthrough=5'])
-  gl_AS_VAR_APPEND([$1], [' -Wshift-overflow=2'])
-  gl_AS_VAR_APPEND([$1], [' -Wuse-after-free=3'])
-  gl_AS_VAR_APPEND([$1], [' -Wunused-const-variable=2'])
-  gl_AS_VAR_APPEND([$1], [' -Wvla-larger-than=4031'])
+  AS_VAR_APPEND([$1], [' -Warray-bounds=2'])
+  AS_VAR_APPEND([$1], [' -Wattribute-alias=2'])
+  AS_VAR_APPEND([$1], [' -Wbidi-chars=any,ucn'])
+  AS_VAR_APPEND([$1], [' -Wformat-overflow=2'])
+  AS_VAR_APPEND([$1], [' -Wformat=2'])
+  AS_VAR_APPEND([$1], [' -Wformat-truncation=2'])
+  AS_VAR_APPEND([$1], [' -Wimplicit-fallthrough=5'])
+  AS_VAR_APPEND([$1], [' -Wshift-overflow=2'])
+  AS_VAR_APPEND([$1], [' -Wuse-after-free=3'])
+  AS_VAR_APPEND([$1], [' -Wunused-const-variable=2'])
+  AS_VAR_APPEND([$1], [' -Wvla-larger-than=4031'])
 
   # These are needed for older GCC versions.
   if test -n "$GCC" && gl_gcc_version=`($CC --version) 2>/dev/null`; then
     case $gl_gcc_version in
       'gcc (GCC) '[[0-3]].* | \
       'gcc (GCC) '4.[[0-7]].*)
-        gl_AS_VAR_APPEND([$1], [' -fdiagnostics-show-option'])
-        gl_AS_VAR_APPEND([$1], [' -funit-at-a-time'])
+        AS_VAR_APPEND([$1], [' -fdiagnostics-show-option'])
+        AS_VAR_APPEND([$1], [' -funit-at-a-time'])
           ;;
     esac
     case $gl_gcc_version in
       'gcc (GCC) '[[0-9]].*)
-        gl_AS_VAR_APPEND([$1], [' -fno-common'])
+        AS_VAR_APPEND([$1], [' -fno-common'])
           ;;
     esac
   fi
 
   # Disable specific options as needed.
   if test "$gl_cv_cc_nomfi_needed" = yes; then
-    gl_AS_VAR_APPEND([$1], [' -Wno-missing-field-initializers'])
+    AS_VAR_APPEND([$1], [' -Wno-missing-field-initializers'])
   fi
 
   if test "$gl_cv_cc_uninitialized_supported" = no; then
-    gl_AS_VAR_APPEND([$1], [' -Wno-uninitialized'])
+    AS_VAR_APPEND([$1], [' -Wno-uninitialized'])
   fi
 
   # This warning have too many false alarms in GCC 11.2.1.
   # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101713
-  gl_AS_VAR_APPEND([$1], [' -Wno-analyzer-malloc-leak'])
+  AS_VAR_APPEND([$1], [' -Wno-analyzer-malloc-leak'])
 
   AC_LANG_POP([C])
 ])
diff --git a/m4/warnings.m4 b/m4/warnings.m4
index 063bc5ca64..76e97907b5 100644
--- a/m4/warnings.m4
+++ b/m4/warnings.m4
@@ -1,4 +1,4 @@
-# warnings.m4 serial 16
+# warnings.m4 serial 17
 dnl Copyright (C) 2008-2023 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -6,14 +6,7 @@
 
 dnl From Simon Josefsson
 
-# gl_AS_VAR_APPEND(VAR, VALUE)
-# ----------------------------
-# Provide the functionality of AS_VAR_APPEND if Autoconf does not have it.
-m4_ifdef([AS_VAR_APPEND],
-[m4_copy([AS_VAR_APPEND], [gl_AS_VAR_APPEND])],
-[m4_define([gl_AS_VAR_APPEND],
-[AS_VAR_SET([$1], [AS_VAR_GET([$1])$2])])])
-
+AC_PREREQ([2.64])
 
 # gl_COMPILER_OPTION_IF(OPTION, [IF-SUPPORTED], [IF-NOT-SUPPORTED],
 #                       [PROGRAM = AC_LANG_PROGRAM()])
@@ -34,7 +27,7 @@ AC_DEFUN([gl_COMPILER_OPTION_IF]
 m4_pushdef([gl_Positive], [$gl_positive])])dnl
 AC_CACHE_CHECK([whether _AC_LANG compiler handles $1], [gl_Warn], [
   gl_save_compiler_FLAGS="$gl_Flags"
-  gl_AS_VAR_APPEND(m4_defn([gl_Flags]),
+  AS_VAR_APPEND(m4_defn([gl_Flags]),
     [" $gl_unknown_warnings_are_errors ]m4_defn([gl_Positive])["])
   AC_LINK_IFELSE([m4_default([$4], [AC_LANG_PROGRAM([[]])])],
                  [AS_VAR_SET([gl_Warn], [yes])],
@@ -97,7 +90,7 @@ AC_DEFUN([gl_UNKNOWN_WARNINGS_ARE_ERRORS_IMPL]
 AC_DEFUN([gl_WARN_ADD],
 [AC_REQUIRE([gl_UNKNOWN_WARNINGS_ARE_ERRORS(]_AC_LANG[)])
 gl_COMPILER_OPTION_IF([$1],
-  [gl_AS_VAR_APPEND(m4_if([$2], [], [[WARN_]_AC_LANG_PREFIX[FLAGS]], [[$2]]), 
[" $1"])],
+  [AS_VAR_APPEND(m4_if([$2], [], [[WARN_]_AC_LANG_PREFIX[FLAGS]], [[$2]]), [" 
$1"])],
   [],
   [$3])
 m4_ifval([$2],