AC_CHECK_HEADERS([ext/hash_map],[
AC_DEFINE([HASH_MAP_CLASS],[HASH_MAP_NAMESPACE::hash_map],[The template name for unordered maps.])
AC_DEFINE([HASH_MAP_H],[<ext/hash_map>],[The header file to include for unordered maps.])
AC_DEFINE([HASH_MAP_NAMESPACE],[__gnu_cxx],[The namespace for unordered maps.])
AC_CHECK_HEADERS([ext/hash_map],[
AC_DEFINE([HASH_MAP_CLASS],[HASH_MAP_NAMESPACE::hash_map],[The template name for unordered maps.])
AC_DEFINE([HASH_MAP_H],[<ext/hash_map>],[The header file to include for unordered maps.])
AC_DEFINE([HASH_MAP_NAMESPACE],[__gnu_cxx],[The namespace for unordered maps.])