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/Serialization/ASTWriter.cpp b/lib/Serialization/ASTWriter.cpp
index f33fbc2..09c5bbb 100644
--- a/lib/Serialization/ASTWriter.cpp
+++ b/lib/Serialization/ASTWriter.cpp
@@ -353,7 +353,7 @@
 
 void ASTTypeWriter::VisitPackExpansionType(const PackExpansionType *T) {
   Writer.AddTypeRef(T->getPattern(), Record);
-  if (llvm::Optional<unsigned> NumExpansions = T->getNumExpansions())
+  if (Optional<unsigned> NumExpansions = T->getNumExpansions())
     Record.push_back(*NumExpansions + 1);
   else
     Record.push_back(0);
@@ -3301,11 +3301,11 @@
 void ASTWriter::AddVersionTuple(const VersionTuple &Version,
                                 RecordDataImpl &Record) {
   Record.push_back(Version.getMajor());
-  if (llvm::Optional<unsigned> Minor = Version.getMinor())
+  if (Optional<unsigned> Minor = Version.getMinor())
     Record.push_back(*Minor + 1);
   else
     Record.push_back(0);
-  if (llvm::Optional<unsigned> Subminor = Version.getSubminor())
+  if (Optional<unsigned> Subminor = Version.getSubminor())
     Record.push_back(*Subminor + 1);
   else
     Record.push_back(0);
@@ -4463,7 +4463,7 @@
     break;
   case TemplateArgument::TemplateExpansion:
     AddTemplateName(Arg.getAsTemplateOrTemplatePattern(), Record);
-    if (llvm::Optional<unsigned> NumExpansions = Arg.getNumTemplateExpansions())
+    if (Optional<unsigned> NumExpansions = Arg.getNumTemplateExpansions())
       Record.push_back(*NumExpansions + 1);
     else
       Record.push_back(0);