The "unifdef" program used by uClibc during install unconditionally uses the optional verrx() family of functions, which are optional in uClibc, controlled by the UCLIBC_HAS_BSD_ERR flag. This means that a stock uClibc, built with UCLIBC_HAS_BSD_ERR off, cannot be used to recompile itself.
fixed with fa6b1e952629879dd715730637ffa3b45eb83285