PATCH, libiberty: eliminate build warning

[Ian Lance Taylor]

John Reiser <jreiser@bitwagon.com> writes:

>>         * pex-unix.c (pex_child_error): Improve warning avoidance by
>>         checking the results of write(3) and exiting with -2 if any write
>>         returns a non-zero value.
>
>> +#define writeerr(s) retval |= write (STDERR_FILE_NO, s, strlen (s))
>
>> +  _exit (retval == 0 ? -1 : -2);
>
> Calling _exit(-1) will be exceedingly rare.

It's all a pointless exercise to avoid a useless gcc warning triggered
by over-eager Debian header files.  I think this bikeshed has been
painted enough.

Ian