diff --git a/m4/ax_prefix_config_h.m4 b/m4/ax_prefix_config_h.m4
new file mode 100644
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--- /dev/null
+++ b/m4/ax_prefix_config_h.m4
@@ -0,0 +1,209 @@
+# ===========================================================================
+#    http://www.gnu.org/software/autoconf-archive/ax_prefix_config_h.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_PREFIX_CONFIG_H [(OUTPUT-HEADER [,PREFIX [,ORIG-HEADER]])]
+#
+# DESCRIPTION
+#
+#   This is a new variant from ac_prefix_config_ this one will use a
+#   lowercase-prefix if the config-define was starting with a
+#   lowercase-char, e.g. "#define const", "#define restrict", or "#define
+#   off_t", (and this one can live in another directory, e.g.
+#   testpkg/config.h therefore I decided to move the output-header to be the
+#   first arg)
+#
+#   takes the usual config.h generated header file; looks for each of the
+#   generated "#define SOMEDEF" lines, and prefixes the defined name (ie.
+#   makes it "#define PREFIX_SOMEDEF". The result is written to the output
+#   config.header file. The PREFIX is converted to uppercase for the
+#   conversions.
+#
+#   Defaults:
+#
+#     OUTPUT-HEADER = $PACKAGE-config.h
+#     PREFIX = $PACKAGE
+#     ORIG-HEADER, from AM_CONFIG_HEADER(config.h)
+#
+#   Your configure.ac script should contain both macros in this order, and
+#   unlike the earlier variations of this prefix-macro it is okay to place
+#   the AX_PREFIX_CONFIG_H call before the AC_OUTPUT invokation.
+#
+#   Example:
+#
+#     AC_INIT(config.h.in)        # config.h.in as created by "autoheader"
+#     AM_INIT_AUTOMAKE(testpkg, 0.1.1)    # makes #undef VERSION and PACKAGE
+#     AM_CONFIG_HEADER(config.h)          # prep config.h from config.h.in
+#     AX_PREFIX_CONFIG_H(mylib/_config.h) # prep mylib/_config.h from it..
+#     AC_MEMORY_H                         # makes "#undef NEED_MEMORY_H"
+#     AC_C_CONST_H                        # makes "#undef const"
+#     AC_OUTPUT(Makefile)                 # creates the "config.h" now
+#                                         # and also mylib/_config.h
+#
+#   if the argument to AX_PREFIX_CONFIG_H would have been omitted then the
+#   default outputfile would have been called simply "testpkg-config.h", but
+#   even under the name "mylib/_config.h" it contains prefix-defines like
+#
+#     #ifndef TESTPKG_VERSION
+#     #define TESTPKG_VERSION "0.1.1"
+#     #endif
+#     #ifndef TESTPKG_NEED_MEMORY_H
+#     #define TESTPKG_NEED_MEMORY_H 1
+#     #endif
+#     #ifndef _testpkg_const
+#     #define _testpkg_const _const
+#     #endif
+#
+#   and this "mylib/_config.h" can be installed along with other
+#   header-files, which is most convenient when creating a shared library
+#   (that has some headers) where some functionality is dependent on the
+#   OS-features detected at compile-time. No need to invent some
+#   "mylib-confdefs.h.in" manually. :-)
+#
+#   Note that some AC_DEFINEs that end up in the config.h file are actually
+#   self-referential - e.g. AC_C_INLINE, AC_C_CONST, and the AC_TYPE_OFF_T
+#   say that they "will define inline|const|off_t if the system does not do
+#   it by itself". You might want to clean up about these - consider an
+#   extra mylib/conf.h that reads something like:
+#
+#     #include <mylib/_config.h>
+#     #ifndef _testpkg_const
+#     #define _testpkg_const const
+#     #endif
+#
+#   and then start using _testpkg_const in the header files. That is also a
+#   good thing to differentiate whether some library-user has starting to
+#   take up with a different compiler, so perhaps it could read something
+#   like this:
+#
+#     #ifdef _MSC_VER
+#     #include <mylib/_msvc.h>
+#     #else
+#     #include <mylib/_config.h>
+#     #endif
+#     #ifndef _testpkg_const
+#     #define _testpkg_const const
+#     #endif
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Guido U. Draheim <guidod@gmx.de>
+#   Copyright (c) 2008 Marten Svantesson
+#   Copyright (c) 2008 Gerald Point <Gerald.Point@labri.fr>
+#
+#   This program is free software; you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation; either version 3 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 11
+
+AC_DEFUN([AX_PREFIX_CONFIG_H],[dnl
+AC_PREREQ([2.62])
+AC_BEFORE([AC_CONFIG_HEADERS],[$0])dnl
+AC_CONFIG_COMMANDS([ifelse($1,,$PACKAGE-config.h,$1)],[dnl
+AS_VAR_PUSHDEF([_OUT],[ac_prefix_conf_OUT])dnl
+AS_VAR_PUSHDEF([_DEF],[ac_prefix_conf_DEF])dnl
+AS_VAR_PUSHDEF([_PKG],[ac_prefix_conf_PKG])dnl
+AS_VAR_PUSHDEF([_LOW],[ac_prefix_conf_LOW])dnl
+AS_VAR_PUSHDEF([_UPP],[ac_prefix_conf_UPP])dnl
+AS_VAR_PUSHDEF([_INP],[ac_prefix_conf_INP])dnl
+m4_pushdef([_script],[conftest.prefix])dnl
+m4_pushdef([_symbol],[m4_cr_Letters[]m4_cr_digits[]_])dnl
+_OUT=`echo ifelse($1, , $PACKAGE-config.h, $1)`
+_DEF=`echo _$_OUT | sed -e "y:m4_cr_letters:m4_cr_LETTERS[]:" -e "s/@<:@^m4_cr_Letters@:>@/_/g"`
+_PKG=`echo ifelse($2, , $PACKAGE, $2)`
+_LOW=`echo _$_PKG | sed -e "y:m4_cr_LETTERS-:m4_cr_letters[]_:"`
+_UPP=`echo $_PKG | sed -e "y:m4_cr_letters-:m4_cr_LETTERS[]_:"  -e "/^@<:@m4_cr_digits@:>@/s/^/_/"`
+_INP=`echo "ifelse($3,,,$3)" | sed -e 's/ *//'`
+if test ".$_INP" = "."; then
+   for ac_file in : $CONFIG_HEADERS; do test "_$ac_file" = _: && continue
+     case "$ac_file" in
+        *.h) _INP=$ac_file ;;
+        *)
+     esac
+     test ".$_INP" != "." && break
+   done
+fi
+if test ".$_INP" = "."; then
+   case "$_OUT" in
+      */*) _INP=`basename "$_OUT"`
+      ;;
+      *-*) _INP=`echo "$_OUT" | sed -e "s/@<:@_symbol@:>@*-//"`
+      ;;
+      *) _INP=config.h
+      ;;
+   esac
+fi
+if test -z "$_PKG" ; then
+   AC_MSG_ERROR([no prefix for _PREFIX_PKG_CONFIG_H])
+else
+  if test ! -f "$_INP" ; then if test -f "$srcdir/$_INP" ; then
+     _INP="$srcdir/$_INP"
+  fi fi
+  AC_MSG_NOTICE(creating $_OUT - prefix $_UPP for $_INP defines)
+  if test -f $_INP ; then
+    AS_ECHO(["s/^@%:@undef  *\\(@<:@m4_cr_LETTERS[]_@:>@\\)/@%:@undef $_UPP""_\\1/"]) > _script
+    AS_ECHO(["s/^@%:@undef  *\\(@<:@m4_cr_letters@:>@\\)/@%:@undef $_LOW""_\\1/"]) >> _script
+    AS_ECHO(["s/^@%:@def[]ine  *\\(@<:@m4_cr_LETTERS[]_@:>@@<:@_symbol@:>@*\\)\\(.*\\)/@%:@ifndef $_UPP""_\\1\\"]) >> _script
+    AS_ECHO(["@%:@def[]ine $_UPP""_\\1\\2\\"]) >> _script
+    AS_ECHO(["@%:@endif/"]) >> _script
+    AS_ECHO(["s/^@%:@def[]ine  *\\(@<:@m4_cr_letters@:>@@<:@_symbol@:>@*\\)\\(.*\\)/@%:@ifndef $_LOW""_\\1\\"]) >> _script
+    AS_ECHO(["@%:@define $_LOW""_\\1\\2\\"]) >> _script
+    AS_ECHO(["@%:@endif/"]) >> _script
+    # now executing _script on _DEF input to create _OUT output file
+    echo "@%:@ifndef $_DEF"      >$tmp/pconfig.h
+    echo "@%:@def[]ine $_DEF 1" >>$tmp/pconfig.h
+    echo ' ' >>$tmp/pconfig.h
+    echo /'*' $_OUT. Generated automatically at end of configure. '*'/ >>$tmp/pconfig.h
+
+    sed -f _script $_INP >>$tmp/pconfig.h
+    echo ' ' >>$tmp/pconfig.h
+    echo '/* once:' $_DEF '*/' >>$tmp/pconfig.h
+    echo "@%:@endif" >>$tmp/pconfig.h
+    if cmp -s $_OUT $tmp/pconfig.h 2>/dev/null; then
+      AC_MSG_NOTICE([$_OUT is unchanged])
+    else
+      ac_dir=`AS_DIRNAME(["$_OUT"])`
+      AS_MKDIR_P(["$ac_dir"])
+      rm -f "$_OUT"
+      mv $tmp/pconfig.h "$_OUT"
+    fi
+    cp _script _configs.sed
+  else
+    AC_MSG_ERROR([input file $_INP does not exist - skip generating $_OUT])
+  fi
+  rm -f conftest.*
+fi
+m4_popdef([_symbol])dnl
+m4_popdef([_script])dnl
+AS_VAR_POPDEF([_INP])dnl
+AS_VAR_POPDEF([_UPP])dnl
+AS_VAR_POPDEF([_LOW])dnl
+AS_VAR_POPDEF([_PKG])dnl
+AS_VAR_POPDEF([_DEF])dnl
+AS_VAR_POPDEF([_OUT])dnl
+],[PACKAGE="$PACKAGE"])])