AX_C___ATTRIBUTE__
AC_FUNC_FORK
-AC_CHECK_FUNCS([memmove setenv])
+AC_CHECK_FUNCS([memmove setenv],
+ [],[AC_MSG_ERROR([function is required])])
dnl Thanks to gperftools' configure.ac (https://code.google.com/p/gperftools).
AC_MSG_CHECKING([for __builtin_expect])