[tests] Add host-byteorder-*-endian; update XFAILs of big-endian triples
Triple components in XFAIL lines are tested against the target triple.
Various tests that are expected to fail on big-endian hosts are marked
as being XFAIL for big-endian targets. This patch corrects these tests
by having them test against a new host-byteorder-big-endian feature.
Reviewers: xingxue, sfertile, jasonliu
Reviewed By: xingxue
Subscribers: jvesely, nhaehnle, fedor.sergeev, llvm-commits
Differential Revision: https://reviews.llvm.org/D60551