Compile CanvasKit without -fPIC, for latest emscripten compatibility.

Due to an issue in emscripten's latest-upstream compiler (link below),
Skia's libraries can't be built using -fPIC. This change allows users
to opt-out of using -fPIC during compilation, and sets compile.sh to
opt-out accordingly.
https://github.com/emscripten-core/emscripten/issues/8995
https://github.com/emscripten-core/emscripten/issues/9317

Change-Id: I25b6e185b58ab1ba8263f2e2f450591f6025f62c
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/243317
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
2 files changed