i.e. not depending on the first fd to be 4.

libiconv expects program_invocation_name to be an lvalue

The sigaction handler called map on an option, creating a pointer to a
move value. This in turned caused UB for signal handlers. Avoid using
pointers directly, and instead prefer references.

It's happening...

WIP mainly because we *should* use thread locals, but #[thread_local]
causes segfaults.