[canvaskit] Update build script to support latest Emscripten

Add workaround for https://github.com/emscripten-core/emscripten/issues/10072

Note to reviewer, please check out the steps I added
in canvaskit/README.md to document this process.

Bug: skia:9816
Change-Id: Idbe7ff08ac62f4f4d70e656384831b8d24c4a684
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/266941
Reviewed-by: Eric Boren <borenet@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
23 files changed