Add big-endian defines into base/build/build_config.h

Forgot to add into https://weave-review.googlesource.com/#/c/1632/

BUG=25017606

Change-Id: I146b5e540e9876eb44718e23bcda047806a80116
Reviewed-on: https://weave-review.googlesource.com/1652
Reviewed-by: Vitaly Buka <vitalybuka@google.com>
1 file changed