getrlimit, setrlimit

[Matthew Fluet]

>       type rlimit = int

I trace rlim_t back to an unsigned long (or an unsigned quad long, if
__USE_FILE_OFFSET64 is defined), so maybe Word32.word is a better choice.

Also, you might include
        val infinity : rlimit
and
        val infinity = _prim "RLIM_INFINITY";