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

llvm-svn: 63271
diff --git a/clang/lib/Lex/PPLexerChange.cpp b/clang/lib/Lex/PPLexerChange.cpp
index f00283b..3e02fbd 100644
--- a/clang/lib/Lex/PPLexerChange.cpp
+++ b/clang/lib/Lex/PPLexerChange.cpp
@@ -15,7 +15,7 @@
 #include "clang/Lex/Preprocessor.h"
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/MacroInfo.h"
-#include "clang/Basic/DiagnosticLex.h"
+#include "clang/Lex/LexDiagnostic.h"
 #include "clang/Basic/SourceManager.h"
 #include "llvm/Support/MemoryBuffer.h"