LU-4674 endianness: Fix __{LITTLE,BIG}_ENDIAN macro usage

LU-4674 endianness: Fix __{LITTLE,BIG}_ENDIAN macro usage

Fixed the userspace code where __{LITTLE,BIG}_ENDIAN is tested
with #ifdef. This patch replaces those checks
with #if __BYTE_ORDER == __{LITTLE,BIG}_ENDIAN

Signed-off-by: Swapnil Pimpale <spimpale@ddn.com>
Change-Id: I92d4cf0c880d8032ea5023cb47ccfe7236dd03ab
Reviewed-on: http://review.whamcloud.com/9641
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>