Include llvm::Optional in clang/Basic/LLVM.h

Post-commit CR feedback from Jordan Rose regarding r175594.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175679 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaExprObjC.cpp b/lib/Sema/SemaExprObjC.cpp
index 76ee983..c0df318 100644
--- a/lib/Sema/SemaExprObjC.cpp
+++ b/lib/Sema/SemaExprObjC.cpp
@@ -170,9 +170,9 @@
                                                 QualType NumberType,
                                                 bool isLiteral = false,
                                                 SourceRange R = SourceRange()) {
-  llvm::Optional<NSAPI::NSNumberLiteralMethodKind> Kind 
-    = S.NSAPIObj->getNSNumberFactoryMethodKind(NumberType);
-  
+  Optional<NSAPI::NSNumberLiteralMethodKind> Kind =
+      S.NSAPIObj->getNSNumberFactoryMethodKind(NumberType);
+
   if (!Kind) {
     if (isLiteral) {
       S.Diag(Loc, diag::err_invalid_nsnumber_type)