fix: do not use linux32 when unnecessary

[mayeut]

The linux32 command is always used for linux i686.
This makes cross building from macOS arm64 impossible at the moment (might depend on docker configuration).

This PR proposes to check the architecture seen inside the container before using (or not) the linux32 command.

[joerick]

Interesting. Is this a fix for the '-mnative' error on macOS?

[joerick]

i686 is the only 32-bit arch so far, I think. Perhaps it would be easier to match that directly?

[mayeut]

Is this a fix for the '-mnative' error on macOS?

No, it's a fix for a deadlock following a call to linux32:

WARNING: The requested image's platform (linux/386) does not match the detected host platform (linux/arm64/v8) and no specific platform was requested
3fca67068b8d0aa05202598ccb3d9e80a27327038b85ede10fb6ab3f73b7543e
    + /bin/true
linux32: Failed to set personality to linux32: Invalid argument

I think that the ENTRYPOINT isn't used when you specify a program via run or create?

It's definitely used on run, the program specified via run is passed to the entrypoint. I'll check it's passed via create also and add a test for this.

Turning this into draft until I get time to address all comments.

[joerick]

It's definitely used on run, the program specified via run is passed to the entrypoint. I'll check it's passed via create also and add a test for this.

Ah, perhaps I am confused about the difference between CMD and ENTRYPOINT.

[mayeut]

I checked https://docs.docker.com/engine/reference/commandline/create/ and since the ENTRYPOINT can be overridden (same as with run), it's used.
So the confusion might indeed come from ENTRYPOINT vs CMD (which is indeed overriden when specifying a custom command).

[mayeut]

Reaching disk space limits once again. I'll add different commits to free some space.

[mayeut]

seems cirrus-ci windows x86 is having troubles, found cirruslabs/cirrus-ci-docs#1232

edit: this is now fixed.

[joerick]

looks good to me!