Move a method from IdentifierTable.h out of line and remove the SmallString include.

Fix all the transitive include users.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149783 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Serialization/ASTReaderStmt.cpp b/lib/Serialization/ASTReaderStmt.cpp
index 623ee1f..24da01a 100644
--- a/lib/Serialization/ASTReaderStmt.cpp
+++ b/lib/Serialization/ASTReaderStmt.cpp
@@ -16,6 +16,7 @@
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclTemplate.h"
 #include "clang/AST/StmtVisitor.h"
+#include "llvm/ADT/SmallString.h"
 using namespace clang;
 using namespace clang::serialization;