2nd OSMem.c fix for rlimit crash

OSMem.c

#if defined(HAVE_SYS_RESOURCE_H) && defined(HAVE_SYS_TIME_H)
    struct rlimit asLimit;
    /* rlim_t is signed on some platforms, including FreeBSD;
     * explicitly cast to avoid sign compare error */
    if (!getrlimit(RLIMIT_AS, &asLimit)
        && asLimit.rlim_cur > 0
        && *len > (W_) asLimit.rlim_cur) {

        // TODO: get stack limit from pthread_attr_getstacksize
        struct rlimit stackLimit;
        if (getrlimit(RLIMIT_STACK, &stackLimit)) {
            // Default stack size on Linux is 8MB
            stackLimit.rlim_cur = 8388608;
            debugBelch("Setting default stack limit\n");
        } else {
            debugBelch("Stack limit is: %zu\n", stackLimit.rlim_cur);
        }

        size_t pageSize = getPageSize();
        // 2/3rds of limit, round down to multiple of PAGE_SIZE
        W_ *len = ((asLimit.rlim_cur * ((double) 2/3)) / pageSize) * pageSize;

        if (((W_) (asLimit.rlim_cur - *len )) < ((W_) (stackLimit.rlim_cur * 3))) {
            sysErrorBelch("not enough available virtual memory! Please check your resource limits!");
        }
    }
#endif