Keep the obj_mac.h license header round-tripping.

Probably best to keep the original format, trailing whitespace and all.

Change-Id: I81a0ac46fd4ab4bb9d2b03d930b191024971447c
Reviewed-on: https://boringssl-review.googlesource.com/2473
Reviewed-by: Adam Langley <agl@google.com>