move library-specific diagnostic headers into library private dirs.  Reduce
redundant #includes.  Patch by Anders Johnsen!

llvm-svn: 63271
diff --git a/clang/lib/AST/ExprConstant.cpp b/clang/lib/AST/ExprConstant.cpp
index c444a19..f07df0a 100644
--- a/clang/lib/AST/ExprConstant.cpp
+++ b/clang/lib/AST/ExprConstant.cpp
@@ -15,7 +15,7 @@
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/RecordLayout.h"
 #include "clang/AST/StmtVisitor.h"
-#include "clang/Basic/DiagnosticAST.h"
+#include "clang/AST/ASTDiagnostic.h"
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/Support/Compiler.h"
 using namespace clang;