+ AC_CACHE_CHECK([whether _XOPEN_SOURCE should be defined],
+ [ac_cv_should_define__xopen_source],
+ [ac_cv_should_define__xopen_source=no
+ AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM([[
+ #include <wchar.h>
+ mbstate_t x;]])],
+ [],
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM([[
+ #define _XOPEN_SOURCE 500
+ #include <wchar.h>
+ mbstate_t x;]])],
+ [ac_cv_should_define__xopen_source=yes])])])
+ test $ac_cv_should_define__xopen_source = yes &&
+ AC_DEFINE([_XOPEN_SOURCE], [500])