Update autoconfig/config.{sub,guess} to the latest version

from the GNU upstream: git://git.savannah.gnu.org/config.git

1. It eliminates a local LLVM patch for auroraux (because, the
mainline config.sub has already got support of auroraux)
2. It adds several new recognized target cpus and operating systems
(in particular, PNaCl)

llvm-svn: 137984