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/PreprocessorLexer.cpp b/clang/lib/Lex/PreprocessorLexer.cpp
index f75ce42..f9dfad9 100644
--- a/clang/lib/Lex/PreprocessorLexer.cpp
+++ b/clang/lib/Lex/PreprocessorLexer.cpp
@@ -13,7 +13,7 @@
 
 #include "clang/Lex/PreprocessorLexer.h"
 #include "clang/Lex/Preprocessor.h"
-#include "clang/Basic/DiagnosticLex.h"
+#include "clang/Lex/LexDiagnostic.h"
 #include "clang/Basic/SourceManager.h"
 using namespace clang;