message: Add word size detection to Platform.h
diff: # error "Unsupported platform."
  #endif
  +#if defined(_WIN64) || defined(__aarch64__) || defined(__x86_64__)
  +# define NXT_PLATFORM_64_BIT 1
  +static_assert(sizeof(sizeof(char)) == 8, "Expect sizeof(size_t) == 8");
  +#elif defined(_WIN32) || defined(__i386__) || defined(__arm__)
  +# define NXT_PLATFORM_32_BIT 1
  +static_assert(sizeof(sizeof(char)) == 4, "Expect sizeof(size_t) == 4");
  +#else
  +# error "Unsupported platform"
  +#endif
  +
  #endif // COMMON_PLATFORM_H_
  