use __BYTE_ORDER__ macro to detect endianness when available

BUG=skia:

Change-Id: Iff27097c248a643319e930a6212c5a7155bd0064
Reviewed-on: https://skia-review.googlesource.com/5280
Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Mike Klein <mtklein@chromium.org>
1 file changed