Add support for Ubuntu 26.04 (liblttng-ust1t64, libicu77-80)

[dvaldivia]

Summary

Ubuntu 26.04 LTS (VERSION_CODENAME=resolute, "Resolute Raccoon") completes the time_t 64-bit transition for liblttng-ust and ships a newer libicu. On a fresh 26.04 install the existing apt_get_with_fallbacks chains cannot resolve either dependency, so ./bin/installdependencies.sh aborts with Can't install dotnet core dependencies. before the runner can configure.

This PR extends both fallback chains so the script keeps working on 26.04 while remaining a no-op on older releases (the helper silently skips packages that aren't in the apt index).

What changed

src/Misc/layoutbin/installdependencies.sh

Chain	Before	After
LTTng	liblttng-ust1 liblttng-ust0	liblttng-ust1t64 liblttng-ust1 liblttng-ust0
ICU	libicu76 ... libicu52	libicu80 libicu79 libicu78 libicu77 libicu76 ... libicu52

docs/start/envlinux.md — matching dependency list.

Why these specific names

Verified directly inside ubuntu:26.04:

$ apt-cache search '^liblttng-ust' | grep -E 'liblttng-ust[0-9]'
liblttng-ust1t64 - LTTng 2.0 Userspace Tracer (tracing libraries)

$ apt-cache search '^libicu[0-9]+$'
libicu78 - International Components for Unicode

Adding libicu77/79/80 gives runway in case 26.04's archive ICU version changes before GA, and matches the existing pattern of listing several adjacent versions.

Test plan

• Ran the patched script inside ubuntu:26.04 on linux/arm64 — exits with Finish Install Dependencies, installs liblttng-ust1t64 2.14.0-1.1 and libicu78 78.2-2ubuntu1
• Same run on linux/amd64 (via buildx + QEMU) — same result, installs liblttng-ust1t64:amd64 and libicu78:amd64
• Verified the additions are no-ops on older Ubuntu releases — fallbacks fall through harmlessly to the existing liblttng-ust1 / libicu74 etc.

Notes

The libssl3t64 chain already covers 26.04 (also ships libssl3t64). libkrb5-3 and zlib1g package names are unchanged on 26.04. No other changes needed.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Extends the Debian/Ubuntu dependency fallback lists used by the self-hosted runner’s installdependencies.sh script to support Ubuntu 26.04’s time_t transition package naming (liblttng-ust1t64) and newer ICU versions, and updates the Linux prerequisites documentation to match.

Changes:

• Add liblttng-ust1t64 to the LTTng apt fallback chain.
• Add libicu77–libicu80 to the ICU apt fallback chain.
• Update docs/start/envlinux.md dependency list accordingly.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/Misc/layoutbin/installdependencies.sh	Extends apt fallback chains for LTTng and ICU to cover Ubuntu 26.04 package names/versions.
docs/start/envlinux.md	Updates documented Debian/Ubuntu dependency list to match the script changes.

[Copilot]

The punctuation here is a bit ambiguous: using a comma before “liblttng-ust1” can read like multiple packages are required. Consider rephrasing to make the alternation explicit (e.g., “liblttng-ust1t64, liblttng-ust1, or liblttng-ust0” or “liblttng-ust1t64 or liblttng-ust1 or liblttng-ust0”).

Suggested change

	- liblttng-ust1t64, liblttng-ust1 or liblttng-ust0
	- liblttng-ust1t64 or liblttng-ust1 or liblttng-ust0