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/Algorithm.h

@@ -26,4 +26,4 @@ namespace swift {
   }
 } // end namespace swift
 
-#endif /* SWIFT_BASIC_ALGORITHM_H */
+#endif // SWIFT_BASIC_ALGORITHM_H