[PATCH] Fix bug-if1 compilation

[Roland McGrath]

> bug-if1 lacks a prototype for strerror_r.

I put in the fix.  Thanks.

> FYI: the test fails for me on about 50% of the test boxes
> with invalid index returned result "eth1" (with interface names which are
> down).

There is already an open bugzilla item for this, though I haven't looked
into it.  http://sources.redhat.com/bugzilla/show_bug.cgi?id=232


Thanks,
Roland