##### http://autoconf-archive.cryp.to/ac_cxx_have_ext_hash_set.html
#
# SYNOPSIS
#
#   AC_CXX_HAVE_EXT_HASH_SET
#
# DESCRIPTION
#
#   Check if the compiler has ext/hash_set Eg:
#
#     #if defined(HAVE_EXT_HASH_SET)
#     #include <ext/hash_set>
#     #else
#     #if defined(HAVE_STL)
#     #include <hash_set>
#     #else
#     # Can't find hash_set header !
#     #endif
#     #endif
#
# LAST MODIFICATION
#
#   2002-09-04
#
# COPYLEFT
#
#   Copyright (c) 2002 Alain BARBET <alian@cpan.org>
#
#   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 2 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, write to the Free Software
#   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
#   02111-1307, USA.
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#   modified version as well.

AC_DEFUN([AC_CXX_HAVE_EXT_HASH_SET],
[AC_CACHE_CHECK(whether the compiler has ext/hash_set,
ac_cv_cxx_have_ext_hash_set,
[AC_REQUIRE([AC_CXX_NAMESPACES])
  AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  AC_TRY_COMPILE([#include <ext/hash_set>
#ifdef HAVE_NAMESPACES
using namespace std;
#endif],[hash_set<int> t; return 0;],
  ac_cv_cxx_have_ext_hash_set=yes, ac_cv_cxx_have_ext_hash_set=no)
  AC_LANG_RESTORE
])
if test "$ac_cv_cxx_have_ext_hash_set" = yes; then
   AC_DEFINE(HAVE_EXT_HASH_SET,,[define if the compiler has ext/hash_set])
fi
])