Auto merge of #102530 - cuviper:upgrade-i586-gnu, r=pietroalbini

Upgrade dist-i586-gnu-i586-i686-musl to ubuntu:22.04

The system GCC 5 in ubuntu:16.04 will be too old to compile LLVM 16, so
we need an upgrade. To avoid raising the minimum glibc requirements for
`i586-unknown-linux-gnu`, this target is converted to a crosstool-ng
toolchain, *relaxing* it to the same Linux 3.2 / glibc 2.17 minimum we
use elsewhere. The musl targets still use Ubuntu's system toolchain, but
this doesn't have the same compatibility concerns.

Author: bors