gh-151929: Add pythoninfo-build command to Platforms/emscripten

[vstinner]

Add also "pythoninfo-host" command.

• Issue: "wasm32-wasi 3.x" buildbot times out on building Python #151929

[vstinner]

pythoninfo-build displays the 3 new system. keys which can help debugging issues: detect on which machine the job was ran and detect when the machine has been rebooted.

Examples:

CC.version: gcc (Ubuntu 13.3.0-6ubuntu2~24.04.1) 13.3.0
...
sys.version: 3.16.0a0 (remotes/pull/152210/merge-dirty:ee07825, Jun 25 2026, 14:57:29) [GCC 13.3.0]
...
system.boot_id: 02b5e273-98cf-4f41-87ce-cbabd3479518
system.machine_id: b9d4e40b90bc4dcb974f6d60e5fb946e
system.uptime: 0:03:15

[vstinner]

@hoodmane: Would you mind to review this change?

My plan is to backport this change to 3.13, 3.14 and 3.15 branches, and then update the buildbot configuration to call these new commands. And once buildbots are migrated, remove the legacy run --pythoninfo command (at least in the main branch).

[vstinner]

I wrote a similar change for WASI: #152136.

[hoodmane]

Can you explain the relationship to issue #151929? It's not obvious to me.

[hoodmane]

Looks reasonable to me.

[vstinner]

Can you explain the relationship to issue #151929? It's not obvious to me.

I reused the issue gh-151929 to add boot ID, machine ID and uptime to pythoninfo, to help me debugging a performance like the one on the WASI buildbot.

This PR is the Emscripten part of this work.

[vstinner]

Display build info of the build Python:

system.boot_id: 74bf7c41-8422-48f2-910c-f8053609b525
system.machine_id: b9d4e40b90bc4dcb974f6d60e5fb946e
system.uptime: 0:02:07

Display build info of the host/Emscripten Python:

system.machine_id: b9d4e40b90bc4dcb974f6d60e5fb946e

Interesting, the machine ID of the host machine is inherited by the Emscripten filesystem.