rust-intrinsic ABI functions should be unsafe

[brson]

They seem to be safe by default now when other foreign ABI's are unsafe.

Reasonable people disagree.

[alexcrichton]

It seems like some of them like sinf32/logf32/etc probably shouldn't be unsafe. Other ones like forget/init/atomic_* probably should be unsafe.

The safe ones could be re-exported via a non-unsafe function though, because default unsafe is probably more reasonable.

[thestinger]

I would prefer if they were unsafe by default and you could explicitly tag them with #[safe].

[bblum]

nominating backwards-compatible

[bblum]

This seems like it should be a pretty easy change to make, so giving this E-easy. The relevant function to change is check_intrinsic_type in middle/typeck/check/mod.rs.

[bblum]

what, i just had this bug for triage a month ago

[catamorphism]

@brson says this is an implementation detail. De-milestoning

[alexcrichton]

This appears to have been done now, all intrinsics are unsafe.

We can explicitly expose safe versions if we need to.