__builtin_isless, __builtin_islessequal on mips targets

[Nadezhda Ivanоvna Vyukova]

The __builtin_isless, __builtin_islessequal functions are provided as 
implementations of standard C99 functions 'isless', 'isgreater'. Please,
explain why gcc for mips implements them via instructions 

    c.lt.FMT and 
    c.le.FMT 

instead of 

    c.olt.FMT and 
    c.ole.FMT.