Our x86-32 target names are inconsistent

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The typical naming scheme we use for x86-32 targets is:

• i686 means Pentium 4 (yes that makes no sense but, well, it's too disruptive to change now and i786 didn't catch on as a name anywhere), which in particular have SSE2
• i586 means "original Pentium" (no SSE)

We have some targets that violate this:

• i686-linux-android is actually PentiumPro with SSE, but that seems sufficiently close to Pentium 4 that it's still the right name IMO (in particular, it does have more vector extensions than Pentium 4; not sure why we are using "Pentium Pro" as the baseline) (resolved by https://github.com/rust-lang/rust/pull/136885)
• i386-apple-ios uses Penryn as baseline, way newer than Pentium 4, so of course it has SSE (this target is ancient, it predates Rust 1.0)
• i586-pc-nto-qnx700 uses Pentium 4 as baseline (resolved by https://github.com/rust-lang/rust/pull/137324)
• i686-unknown-hurd-gnu uses PentiumPro without SSE as baseline (resolved by https://github.com/rust-lang/rust/pull/136700)
• i686-unknown-redox uses PentiumPro without SSE as baseline (resolved by https://github.com/rust-lang/rust/pull/136698)

If we want to establish the pattern that "i686 has SSE and the rest does not", then the last four of these should be renamed. (These are all tier 3 targets.) I wonder if there is a specific reason that these names were picked diverging from our usual naming scheme, or is it just an oversight because our naming scheme is admittedly not very self-explaining?

• The Apple target is ancient and I assume was picked for consistency with how Apple calls this -- not sure if that should overwrite our own naming scheme.
• For Hurd and Redox, we have no other targets that use PentiumPro without SSE as baseline, so it's a bit unclear what one would even use -- they are somewhere between i586 (original Pentium) and what we call i686 (Pentium 4). The most consistent outcome here would be to use Pentium 4 as the baseline like we use for all other OSes; not sure why Hurd and Redox should be special.
• The i586-pc-nto-qnx700 one however should almost certainly be called i686.

Pinging the listed target maintainers and some other folks:
Cc @bjorn3 @workingjubilee @badboy @deg4uss3r @madsmtm @sthibaul @jackpot51 @flba-eb @gh-tr @jonathanpallant @japaric

Review the target definitions for i386-apple-ios, i686-unknown-hurd-gnu, and i686-unknown-redox, and compare them with the naming convention described in the issue. Read the linked pull requests for the already-resolved targets before deciding which remaining names and baselines are appropriate. Done means the maintainers agree on the naming and the remaining target inconsistencies are addressed.