Set environment for powershell on all platforms

[KiruyaMomochi]

Before this PR

Running . ./emsdk_env.ps1 on Linux PowerShell (pwsh) only output Setting environment variables, but none
of these variables are set actually.

PS /home/kyaru/projects/emsdk> . ./emsdk_env.ps1
Adding directories to PATH: ...
Setting environment variables: ...

PS /home/kyaru/projects/emsdk> emsdk
emsdk: The term 'emsdk' is not recognized as a name of a cmdlet, function, script file, or executable program.
Check the spelling of the name, or if a path was included, verify that the path is correct and try again.

Solution

Decide whether to call write_set_env_script or not by checking current shell, not platform.

After this PR

The script works on all platforms.

PS /home/kyaru/projects/emsdk> . ./emsdk_env.ps1
Adding directories to PATH: ...
Setting environment variables: ...

PS /home/kyaru/projects/emsdk> emsdk
Missing command; Type 'emsdk help' to get a list of commands.

[sbc100]

TIL, you can run powershell outside of windows. Out of interested, on what platform are you running it?

[KiruyaMomochi]

I'm using it on all platforms (Windows, Linux and macOS).

See this GitHub Action file: https://github.com/KiruyaMomochi/AssetStudio/blob/cross/.github/workflows/texture-decoder.yml