Move <optional> into include/experimental, and into the std::experimental namespace, since it's not part of C++14, but of an upcoming TS

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@194867 91177308-0d34-0410-b5e6-96231b3b80d8

test/utilities/optional/optional.object/optional.object.observe/op_arrow.pass.cpp

@@ -15,12 +15,14 @@
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))
 #endif
 
-#include <optional>
+#include <experimental/optional>
 #include <type_traits>
 #include <cassert>
 
 #if _LIBCPP_STD_VER > 11
 
+using std::experimental::optional;
+
 struct X
 {
     int test() const {return 2;}
@@ -33,12 +35,12 @@ int main()
 {
 #if _LIBCPP_STD_VER > 11
     {
-        std::optional<X> opt(X{});
+        optional<X> opt(X{});
         assert(opt->test() == 3);
     }
 #ifdef _LIBCPP_DEBUG
     {
-        std::optional<X> opt;
+        optional<X> opt;
         assert(opt->test() == 3);
         assert(false);
     }