[clang] NFC, move the SourceLocationEncoding.h header guard to the begining of the file

Author: hokein

clang/include/clang/Serialization/SourceLocationEncoding.h

@@ -28,13 +28,13 @@
 //
 //===----------------------------------------------------------------------===//
 
+#ifndef LLVM_CLANG_SERIALIZATION_SOURCELOCATIONENCODING_H
+#define LLVM_CLANG_SERIALIZATION_SOURCELOCATIONENCODING_H
+
 #include "clang/Basic/SourceLocation.h"
 #include "llvm/Support/MathExtras.h"
 #include <climits>
 
-#ifndef LLVM_CLANG_SERIALIZATION_SOURCELOCATIONENCODING_H
-#define LLVM_CLANG_SERIALIZATION_SOURCELOCATIONENCODING_H
-
 namespace clang {
 
 /// Serialized encoding of SourceLocations without context.