Fix wasm builds

After the update to emscripten 1.39.6, source maps don't
work on ASMJS builds and debugger needed the same change
of the default MAIN_MODULE setting as canvaskit and pathkit.

Change-Id: Ifb920dee998ae41fd500adca587b1ad20cfef584
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/267076
Reviewed-by: Kevin Lubick <kjlubick@google.com>
2 files changed