Fix undefined flag for MSAN.

MSAN started failing after https://skia-review.googlesource.com/c/32722.
This should fix it.

No-Try: true
Change-Id: I8956c8c211507923f078fe96921fedaadefae8a8
Reviewed-on: https://skia-review.googlesource.com/32942
Reviewed-by: Ben Wagner <bungeman@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
2 files changed