emsdk_env.sh doesn't work on cygwin due to wrong PATH parsing

[Julianiolo]

the emsdk_env.sh script produces a jumbled up PATH when used under cygwin.

I was able to track the problem down to the wrong ENVPATH_SEPERATOR value beeing picked in emsdk.py (line 126-129).
The standard cygwin shell is bash so it uses ':' instead of ';' to seperate it's PATH, but here it is parsed as if it were using ';'.

I'm not sure how to fix it, I added an extra and not MSYS to the if WINDOWS: line(line 126), and that seemed to work, but I'm not sure if that's the optimal solution.

I'm also not sure what other things might me affected by this problem, everything else besides the mentioned emsdk_env.sh worked for me.

[sbc100]

Feel free to send patches to improve the cygwin support. Sadly we don't have any testing of the cygwin environment, so one thing that would be very useful is adding cynwin to the github CI setup.

[Julianiolo]

#1080 :)

[sbc100]

Are you using the cygwin version or python.exe or a windows version of python.exe? Because in CI we are running under bash.exe, but we are using are native windows version of python.exe (which reports os.environ['PATH'] as with windows path separators)

[Julianiolo]

I'm using the python from cygwin (as you might see in the PR comment), specifically python 3.9.10 on cygwin