[PATCH] Optimize manual byte swap implementations using the GCC bswap builtin

[Ross Ridge]

Nicholas Miell writes:
>Another somewhat common idiom is:
>
>#	define swab32(x)\
>((((uint8_t*)&x)[0] << 24) | (((uint8_t*)&x)[1] << 16) |  \
> (((uint8_t*)&x)[2] << 8)  | (((uint8_t*)&x)[3]))
>
>primarily found in media libraries (a52dec, libdv, libdts, libogmdvd, etc.).

That macro isn't actually a byte swap idiom, it's a big endian read.
It only byte swaps on a little endian machines.

					Ross Ridge