+AC_CHECK_FUNCS([memmove setenv],
+ [],[AC_MSG_ERROR([function is required])])
+AC_CHECK_FUNCS([execvpe])
+dnl These are not in POSIX.
+AC_CHECK_FUNCS([fwrite_unlocked fputs_unlocked fputc_unlocked])
+dnl Internal functions in libc implementations which must be hooked.
+AC_CHECK_FUNCS([__overflow __swbuf])