Expand to an expression evaluating to true in a preprocessor context if the deprecation control macro symbol supplied as an argument has been #define`d as an expression that evaluates to a non‐zero value, and expand to an expression evaluating to `false otherwise. The behavior is undefined unless this macro is evaluated with a single argument having the form of a deprecation control macro symbol, and that symbol has either not been `#define`d at all, or has been `#define`d as nil or an arithmetic expression.