Sort all the #include lines with LLVM's utils/sort_includes.py which
encodes the canonical rules for LLVM's style. I noticed this had drifted
quite a bit when cleaning up LLVM, so wanted to clean up Clang as well.

llvm-svn: 198686
diff --git a/clang/lib/Lex/Preprocessor.cpp b/clang/lib/Lex/Preprocessor.cpp
index 92aeb5c..aa39263 100644
--- a/clang/lib/Lex/Preprocessor.cpp
+++ b/clang/lib/Lex/Preprocessor.cpp
@@ -26,7 +26,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "clang/Lex/Preprocessor.h"
-#include "clang/Lex/MacroArgs.h"
 #include "clang/Basic/FileManager.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
@@ -35,6 +34,7 @@
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/LexDiagnostic.h"
 #include "clang/Lex/LiteralSupport.h"
+#include "clang/Lex/MacroArgs.h"
 #include "clang/Lex/MacroInfo.h"
 #include "clang/Lex/ModuleLoader.h"
 #include "clang/Lex/Pragma.h"
@@ -42,8 +42,8 @@
 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Lex/ScratchBuffer.h"
 #include "llvm/ADT/APFloat.h"
-#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/Support/Capacity.h"
 #include "llvm/Support/ConvertUTF.h"