Tracking Issue for x86 target feature x87 (x87_target_feature)

[RalfJung]

This is a tracking issue for the x86 target feature x87.
The feature gate for the issue is #![feature(x87_target_feature)].

This feature can only be set on softfloat targets; hardfloat targets require it and therefore do not allow toggling it.

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.
Discussion comments will get marked as off-topic or deleted.
Repeated discussions on the tracking issue may lead to the tracking issue getting locked.

Steps

• Implement the RFC (cc @rust-lang/XXX -- can anyone write up mentoring
  instructions?)
• Adjust documentation (see instructions on rustc-dev-guide)
• Formatting for new syntax has been added to the Style Guide (nightly-style-procedure)
• Stabilization PR (see instructions on rustc-dev-guide)

Unresolved Questions

XXX --- list all the "unresolved questions" found in the RFC to ensure they are
not forgotten

Implementation history

[RalfJung]

Never mind, we can just use #44839 like we do for most target feature feature gates.