Canonize swift header files headers and footers

- Added missing ifdef guard in PointerIntEnum header
- Consistent naming convention for ifdef guards
- Consistent 'end namespace swift'
- Consistent single EOL at end of header files

include/swift/Basic/UUID.h

@@ -115,6 +115,6 @@ namespace llvm {
       return a == b;
     }
   };
-}
+} // end namespace swift
 
-#endif
+#endif // SWIFT_BASIC_UUID_H