Attempt to workaround MSVC build issue where I suspect an enum class constant 0 is considered a possible null pointer

I can't reproduce this so far with web compilers, so throwing this at
the bots to see if it sticks.

llvm-svn: 292155

include/llvm/ADT/None.h

@@ -19,7 +19,8 @@
 namespace llvm {
 /// \brief A simple null object to allow implicit construction of Optional<T>
 /// and similar types without having to spell out the specialization's name.
-enum class NoneType { None };
+// (constant value 1 in an attempt to workaround MSVC build issue... )
+enum class NoneType { None = 1 };
 const NoneType None = NoneType::None;
 }