Protect std::experimental::optional tests under libcpp-no-exceptions

In these tests there are some paths that explicitly throw, so use
the TEST_THROW macro that was proposed for this and then skip the tests
that may enter the throwing path.

Differential Revision: https://reviews.llvm.org/D26142



git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@286099 91177308-0d34-0410-b5e6-96231b3b80d8
13 files changed