fix(builder): add ftp.gnu.org fallback for GNU source downloads

[vbelouso]

ftpmirror.gnu.org occasionally redirects to a backend with an expired TLS certificate. curl --retry does not retry SSL errors (exit 60), so the build fails even though the artifact is available elsewhere.

fetch_source now accepts an optional fallback URL. When provided, the preferred source is tried preferred_attempts=3 times (shell loop, retries any curl error). On exhaustion it falls back to the canonical URL with the same retry policy. Without a fallback the existing --retry 10 behaviour is unchanged.

Containerfile exports AUTOCONF/AUTOMAKE/LIBTOOL_FALLBACK_URL=https://ftp.gnu.org/gnu/... for the three affected packages.

[sourcery-ai]

Reviewer's Guide

Adds a fallback mechanism for GNU source downloads in the builder scripts to improve resilience against bad TLS on ftpmirror.gnu.org, wires the new fallback into GNU-related install scripts and the Containerfile, tweaks Arrow build flags for x86_64, and slightly increases the CI test job timeout.

File-Level Changes

Change	Details	Files
Introduce a fallback-aware fetch_source helper that retries a primary URL then an optional fallback URL with robust cleanup and logging, while preserving legacy behavior when no fallback is provided.	Extend fetch_source to accept an optional third argument for a fallback URL in addition to the primary URL. Preserve the original single-URL behavior by keeping curl --retry 10 when no fallback URL is passed. Implement explicit retry loops for both preferred and fallback URLs with up to three attempts each, retrying on any curl failure including TLS errors. On each failed attempt, log the curl exit code and remove any partially downloaded file before retrying. Return early when the target file already exists and propagate the last curl exit code when all attempts fail.	builder/build_scripts/build_utils.sh
Wire GNU package installers to use the new fetch_source fallback support, with Containerfile exporting ftp.gnu.org-based fallback URLs.	Update autoconf, automake, and libtool installer scripts to pass a package-specific fallback URL into fetch_source when defined. Export AUTOCONF_FALLBACK_URL, AUTOMAKE_FALLBACK_URL, and LIBTOOL_FALLBACK_URL in the Containerfile pointing to ftp.gnu.org mirrors for the respective packages.	builder/build_scripts/install-autoconf.sh builder/build_scripts/install-automake.sh builder/build_scripts/install-libtool.sh builder/Containerfile
Adjust Arrow build configuration for x86_64 to avoid linking Boost UUID with libatomic via extra CMake arguments.	Introduce a cmake_extra_args array and detect the target architecture from AUDITWHEEL_ARCH. When building for x86_64, add -DBOOST_UUID_LINK_LIBATOMIC=OFF to the CMake configuration via cmake_extra_args. Append the cmake_extra_args expansion to the existing cmake invocation without changing non-x86_64 builds.	builder/build_scripts/build-arrow.sh
Relax CI constraints slightly by allowing more time for tests to complete.	Increase the GitHub Actions test job timeout from 60 minutes to 90 minutes to reduce spurious failures on slower runs.	.github/workflows/test.yml

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[sourcery-ai]

Hey - I've left some high level feedback:

• The new fetch_source fallback logic hardcodes preferred_attempts and fallback_attempts to 3; consider making these configurable (e.g., via environment variables) so you can tune retry behavior without changing the script.
• In fetch_source, all status messages (including failures and the final 'Both preferred and fallback sources failed') currently go to stdout; routing error-related logs to stderr would make it easier to distinguish build noise from actual failures in CI logs.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- The new fetch_source fallback logic hardcodes preferred_attempts and fallback_attempts to 3; consider making these configurable (e.g., via environment variables) so you can tune retry behavior without changing the script.
- In fetch_source, all status messages (including failures and the final 'Both preferred and fallback sources failed') currently go to stdout; routing error-related logs to stderr would make it easier to distinguish build noise from actual failures in CI logs.

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