Macro cranelift_codegen_meta::predicate

macro_rules! predicate {
    ($a:ident && $($b:tt)*) => { ... };
    (!$a:ident && $($b:tt)*) => { ... };
    (!$a:ident) => { ... };
    ($a:ident) => { ... };
}

A macro that converts boolean settings into predicates to look more natural.