[libcxx] Recover no-exceptions XFAILs - I

First batch of changes to get some of these XFAILs working in the
no-exceptions libc++ variant.

Changed some XFAILs to UNSUPPORTED where the test is all about exception
handling. In other cases, used the test macros TEST_THROW and
TEST_HAS_NO_EXCEPTIONS to conditionally exclude those parts of the test
that concerns exception handling behaviour.

Reviewers: EricWF, mclow.lists

Differential revision: https://reviews.llvm.org/D24562

llvm-svn: 283441