Lots of tests are using an explicit target triple w/o first checking that the
target is actually available. Add a REQUIRES clause to a bunch of them. This should
hopefully unbreak bots which don't configure w/ all targets enabled.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@159949 91177308-0d34-0410-b5e6-96231b3b80d8