[fuzz] Make libfuzzer defines backwards compatible for roll

This should fix the chrome roll.

Change-Id: I2de68f972996bf6124cf5cc27dfd538aa1161057
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/316877
Auto-Submit: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Leon Scroggins <scroggo@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
8 files changed