Fix LLP64 detection in SwapByteOrder.h

MSVC does not define __LONG_MAX__, so we were just getting lucky in this
conditional:
  #if __LONG_MAX__ == __INT_MAX__

Undefined identifiers evaluate to zero in preprocessor conditionals, so
this became true, which happens to work for MSVC platforms.

Instead, use this pattern and let the compiler constant fold:
  return sizeof(long) == sizeof(int) ? SwapByteOrder_32((uint32_t)C)
                                     : SwapByteOrder_64((uint64_t)C);