timeout parameter of the poll() syscall, when negative, must be exactly INFTIM, where defined

[dosshell]

Migrated from GitLab #48

/* On some OSes, typically BSD-based ones, the timeout parameter of the
   poll() syscall, when negative, must be exactly INFTIM, where defined,
   or -1. See issue 31334. */
if (ms < 0) {
#ifdef INFTIM
    ms = INFTIM;
#else
    ms = -1;
#endif
}