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

llvm-svn: 194867
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: dfdac03c8fcd6165795bf8dbce3384ec442ee3d1
diff --git a/src/optional.cpp b/src/optional.cpp
index fde071c..b614d81 100644
--- a/src/optional.cpp
+++ b/src/optional.cpp
@@ -7,10 +7,10 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "optional"
+#include "experimental/optional"
 
 namespace std  // purposefully not using versioning namespace
-{
+{ namespace experimental {
 
 #ifdef _LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS
 
@@ -22,4 +22,4 @@
 
 #endif
 
-}  // std
+}}  // std::experimental