This fixes the Mac launcher, which had been ARM-only. (This launcher is
built from 115.9.0esr, because 115.9.1esr, a recent security fix,
doesn't seem to have a public tag yet.)
The Windows build seems to work without updating the launcher from
115.4.0esr.
We were previously using an old version of the Mozilla updater before they
added Mozilla signature verification, but it's Intel-only, so we need to build
our own version of the current updater with signature verification disabled.
