Move PCHContainerOperations from Frontend to Serialization

Fix a layering violation.  Frontend depends on Serialization, so anything used
by both should be in Serialization.

llvm-svn: 348907
diff --git a/clang/lib/Frontend/ASTUnit.cpp b/clang/lib/Frontend/ASTUnit.cpp
index 05e47af..c7b2551 100644
--- a/clang/lib/Frontend/ASTUnit.cpp
+++ b/clang/lib/Frontend/ASTUnit.cpp
@@ -44,7 +44,6 @@
 #include "clang/Frontend/FrontendDiagnostic.h"
 #include "clang/Frontend/FrontendOptions.h"
 #include "clang/Frontend/MultiplexConsumer.h"
-#include "clang/Frontend/PCHContainerOperations.h"
 #include "clang/Frontend/PrecompiledPreamble.h"
 #include "clang/Frontend/Utils.h"
 #include "clang/Lex/HeaderSearch.h"
@@ -63,6 +62,7 @@
 #include "clang/Serialization/ASTWriter.h"
 #include "clang/Serialization/ContinuousRangeMap.h"
 #include "clang/Serialization/Module.h"
+#include "clang/Serialization/PCHContainerOperations.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/IntrusiveRefCntPtr.h"