Enable LTO in nightly

Enable LTO builds across the nightly pipeline.

Dependencies:

• !31615 (merged) (for the AOSP job)
• !31613 (merged) (for the 32-bit x86 job)

Disabled jobs:

• debian-clang* our or mold issue https://github.com/rui314/mold/issues/1358
• debian-ppc64el broken compiler (not reported)
• debian-arm64-asan pvr issue #11120
• alpine-build-testing not enabled yet, waiting for !31606 (merged)

Builds take longer, as do the runtime of tests in the nightly pipeline, but we are not concerned about the time.

The advantage is that when a build produces broken code, there is a greater chance of reproducing and fixing the issue. When end users report it, it's usually not possible to reproduce the issue.

﹡ where available