1.36 changes the `UnwindSafe` impl precondition for HashMap

[CAD97]

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=0e5a528fc978a90aa15bbf01f68dd1bf

assert_unwind_safe::<HashMap<(), UnsafeCell<()>>>();

Successfully compiles on stable 1.35, fails on beta/pre 1.36.

[CAD97]

First reported to FireFox ESR and shared on irlo here: https://internals.rust-lang.org/t/rust-1-36-0-pre-release-testing/10490/2?u=cad97

[SimonSapin]

rust/src/libstd/panic.rs

Lines 209 to 212 in ef064d2

	#[unstable(feature = "ptr_internals", issue = "0")]
	impl<T: UnwindSafe + ?Sized> UnwindSafe for Unique<T> {}
	#[stable(feature = "nonnull", since = "1.25.0")]
	impl<T: RefUnwindSafe + ?Sized> UnwindSafe for NonNull<T> {}

The UnwindSafe impl for Unique<T> requires T: UnwindSafe, but the one for NonZero<T> requires T: RefUnwindSafe.

[SimonSapin]

#62304 is a possible fix.