pub fn emit_possibility(cfg: &str)Expand description
Indicates to rustc that a config flag should not generate an unexpected_cfgs warning
This looks like cargo:rustc-check-cfg=cfg(VAR)
As of rust 1.80, the compiler does automatic checking of cfgs at compile time.
All custom configuration flags must be known to rustc, or they will generate a warning.
This is done automatically when calling the builtin emit methods on AutoCfg,
but not when calling autocfg::emit directly.
Versions before rust 1.80 will simply ignore this directive.
This function indicates to the compiler that the config flag never has a value. If this is not desired, see [the blog post][check-cfg].