How `std` reaches the operating system

Decided

D-0065, settled by the language’s author: part of spec §18. Older text cites it as 18.65.

extern fn name(…) -> T with no body, allowed only in std, whose body is C++ the compiler ships beside the runtime shim — not in it, so §16.4’s shim still does no I/O. Not generic and not fallible: an extern function is a plain call, and std builds the Error. A program’s own way to C and C++ stays a cpp dependency. First written as a #[native] attribute (r54); a keyword was chosen instead because extern was already reserved and is what C, C++ and Rust readers expect for “the body is elsewhere” (§7.2, §15)