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

test/std/experimental/optional/optional.object/optional.object.observe/value.pass.cpp

@@ -8,7 +8,6 @@
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03, c++11
-// XFAIL: libcpp-no-exceptions
 // <optional>
 
 // T& optional<T>::value();
@@ -17,6 +16,8 @@
 #include <type_traits>
 #include <cassert>
 
+#include "test_macros.h"
+
 using std::experimental::optional;
 using std::experimental::bad_optional_access;
 
@@ -35,6 +36,7 @@ int main()
         opt.emplace();
         assert(opt.value().test() == 4);
     }
+#ifndef TEST_HAS_NO_EXCEPTIONS
     {
         optional<X> opt;
         try
@@ -46,4 +48,5 @@ int main()
         {
         }
     }
+#endif
 }