I've wasted time looking into traits.exp failures a couple of times, only to find out that I was using a rustc built against LLVM 5 -- before the needed infrastructure landed. The llvm version can be detected using "rustc -vV". Then these tests can be xfailed.
There are some enum tests that should also be xfail'd; but before this can be done, we need a release of rustc that has the enum fixes. See https://github.com/rust-lang/rust/pull/54004
... and when the enum xfails are done, some test output can also be tightened up a bit; see bug 23626.
I think this is obsolete now.