Merge branch 'ss/compat-bswap-revamp' into seen

Clean-up compat/bswap.h mess.

Comments?

* ss/compat-bswap-revamp:
  bswap.h: provide a built-in based version of bswap32/64 if possible
  bswap.h: remove optimized x86 version of bswap32/64
  bswap.h: always overwrite ntohl/ntohll macros
  bswap.h: define GIT_LITTLE_ENDIAN on MSVC as little endian
  bswap.h: add support for __BYTE_ORDER__