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/Analysis/FormatString.cpp b/lib/Analysis/FormatString.cpp
index 4b18d8e..10bb9f3 100644
--- a/lib/Analysis/FormatString.cpp
+++ b/lib/Analysis/FormatString.cpp
@@ -527,13 +527,13 @@
   return NULL;
 }
 
-llvm::Optional<ConversionSpecifier>
+Optional<ConversionSpecifier>
 ConversionSpecifier::getStandardSpecifier() const {
   ConversionSpecifier::Kind NewKind;
   
   switch (getKind()) {
   default:
-    return llvm::Optional<ConversionSpecifier>();
+    return Optional<ConversionSpecifier>();
   case DArg:
     NewKind = dArg;
     break;
@@ -756,8 +756,7 @@
   return true;
 }
 
-llvm::Optional<LengthModifier>
-FormatSpecifier::getCorrectedLengthModifier() const {
+Optional<LengthModifier> FormatSpecifier::getCorrectedLengthModifier() const {
   if (CS.isAnyIntArg() || CS.getKind() == ConversionSpecifier::nArg) {
     if (LM.getKind() == LengthModifier::AsLongDouble ||
         LM.getKind() == LengthModifier::AsQuad) {
@@ -767,7 +766,7 @@
     }
   }
 
-  return llvm::Optional<LengthModifier>();
+  return Optional<LengthModifier>();
 }
 
 bool FormatSpecifier::namedTypeToLengthModifier(QualType QT,