Fix CanvasKit warnings compiling on Mac with emsdk 2.0.0

Change-Id: Idcb37644c6c657ce66390ae12d9a55d68abab6cf
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/317642
Commit-Queue: Chris Dalton <csmartdalton@google.com>
Reviewed-by: Kevin Lubick <kjlubick@google.com>
6 files changed