emscripten: upgrade to 1.39.0 + switch to python3
Based on work by @oxr463: https://gitlab.com/oxr463/aports/tree/testing/emscripten-1.38.34
Fixes #10549 (closed).
Edited by Claas Augner
Based on work by @oxr463: https://gitlab.com/oxr463/aports/tree/testing/emscripten-1.38.34
Fixes #10549 (closed).