How to mark a condition is likeyly or unlikey ？

[lili via Digitalmars-d-learn]

Hi：
    In C there has likely unlikely marco used by condition 
expression。
    #define likely(x) __builtin_expect(!!(x), 1)
    #define unlikely(x) __builtin_expect(!!(x), 0)
    if (likely(var > 1)) do...
    How to do this in Dlang？