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/StaticAnalyzer/Checkers/RetainCountChecker.cpp b/lib/StaticAnalyzer/Checkers/RetainCountChecker.cpp
index cb731fc..69191de 100644
--- a/lib/StaticAnalyzer/Checkers/RetainCountChecker.cpp
+++ b/lib/StaticAnalyzer/Checkers/RetainCountChecker.cpp
@@ -3361,8 +3361,7 @@
   //     does not understand.
   ProgramStateRef state = C.getState();
 
-  if (llvm::Optional<loc::MemRegionVal> regionLoc =
-          loc.getAs<loc::MemRegionVal>()) {
+  if (Optional<loc::MemRegionVal> regionLoc = loc.getAs<loc::MemRegionVal>()) {
     escapes = !regionLoc->getRegion()->hasStackStorage();
 
     if (!escapes) {