Mark f16 and f128 as incomplete features.

[tgross35]

See #116909 (comment).

Unfortunately this will probably have a lot that needs to be updated, just getting this started to figure out exactly what that will be.

(moved from #127739, github didn't like my branch typo fix)

r? @scottmcm

[tgross35]

@rustbot label +rla-silenced

[tgross35]

Maybe this isn't super useful if we can get #125016 over the line. That will fix the ABI and linking errors on iirc all but one tier1 platforms, I don't think missing library functions alone are enough to justify this change.

I'll just not prioritize this until at least seeing what happens once that merges (but if somebody wants to push it forward, feel free).

@rustbot author

[tgross35]

Marking the feature incomplete seems like more annoyance & churn than it is worth - the gate is already in > 150 places, across four different rust-lang repos, and there isn't a good solution to the fact that all incomplete features get enabled #127739 (comment). Because of this and because the situation is improving little by little (we can link on most platforms now, yay), I'm just going to close this PR.