libbinder: Fix PAD_SIZE_UNSAFE

// This macro should never be used at runtime, as a too large value

// of s could cause an integer overflow. Instead, you should always

// use the wrapper function pad_size()

#define PAD_SIZE_UNSAFE(s) (((s)+3)&~3)

#define PAD_SIZE_UNSAFE(s) (((s) + 3) & ~3UL)

static size_t pad_size(size_t s) {

    if (s > (std::numeric_limits<size_t>::max() - 3)) {