Make it easier to use emscripten tools

[olilarkin]

Make it easier to use emscripten tools

[trzecieu]

Hi!
Can you please tell me which image do you use? All images have $EMSDK variable being set.

> docker run --rm -it trzeci/emscripten:1.39.16-fastcomp bash -c 'echo $EMSDK'
/emsdk_portable

> docker run --rm -it trzeci/emscripten:1.39.16-upstream bash -c 'echo $EMSDK'
/emsdk_portable

And:

> docker run --rm -it trzeci/emscripten:1.39.16-upstream bash -c ' $EMSDK/upstream/emscripten/tools/file_packager.py --help'
Remember to build the main file with  -s FORCE_FILESYSTEM=1  so that it includes support for loading this file package
Nothing to do!

Just a sanity check:
There is a difference between single quote:

docker run --rm -it trzeci/emscripten:1.39.16-upstream bash -c 'echo $EMSDK'

and double quote:

docker run --rm -it trzeci/emscripten:1.39.16-upstream bash -c "echo $EMSDK"

In case of double quote - the bash interpreter resolves variable before executing the command - effectively it will look for $EMSDK on the host machine, so effectively it will be the same like:

docker run --rm -it trzeci/emscripten:1.39.16-upstream echo $EMSDK

In case of single quote - the string is not interpolated and passed in a raw form to the bash interpreter inside the docker image, and there it will be evaluated - effectively $EMSDK will be resolved to the correct value.