AIX 7.1 defines st_pad[123] to st_[amc]tim.tv_pad, respectively,
breaking declaration of st_pad[123] members in struct solaris_stat.
Undefine them as this is no less terrible than other solutions (like
renaming the fields and losing the binding to Solaris' names).
From: Michael Haubenwallner <haubi@s01en24.gentoo.org>