alter_fp_rounding_mode Is Not Panic Safe #7356

Describe the bug

alter_fp_rounding_mode makes use of fesetround in order to alter the rounding mode on various architectures

let current = fegetround();
fesetround(if UPPER { FE_UPWARD } else { FE_DOWNWARD });
let result = operation(lhs, rhs);
fesetround(current);
result

Unfortunately if operation panics, fesetround will never revert the rounding mode. Drop would be a more reliable way around this, although there are still situations where Drop may not be called

To Reproduce

No response

Expected behavior

Ideally we wouldn't modify global thread-local state at all, but I'm not sure if this can be avoided

Additional context

No response