Function va_copy 

pub unsafe fn va_copy<'f>(dest: *mut VaListImpl<'f>, src: &VaListImpl<'f>)

🔬This is a nightly-only experimental API. (core_intrinsics)

Available on non-crate feature ferrocene_certified only.

Copies the current location of arglist src to the arglist dst.

FIXME: document safety requirements