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

Post-commit CR feedback from Jordan Rose regarding r175594.

llvm-svn: 175679
diff --git a/clang/lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp
index d5203a8..37e203d 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/CallAndMessageChecker.cpp
@@ -134,7 +134,7 @@
   if (!checkUninitFields)
     return false;
 
-  if (llvm::Optional<nonloc::LazyCompoundVal> LV =
+  if (Optional<nonloc::LazyCompoundVal> LV =
           V.getAs<nonloc::LazyCompoundVal>()) {
 
     class FindUninitializedField {