macro to provide this functionality on all platforms

provide a suitable replacement for use in our ISBLANK macro

DNS from /etc/nsswitch.conf, /etc/host.conf or /etc/svc.conf when
/etc/resolv.conf did not exist or was unable to read it.

*) Update CURL_CC_DEBUG_OPTS from curl's script

Include <process.h> for getpid() in ares_init.c.

Added 'optind' and 'optarg' as in adig.c.

<sys/time.h>.

as appropriate for platforms that don't have autotools support

struct, and there are domain/search entries in /etc/resolv.conf, the domains
of the options struct will be overridden.

defining HAVE_SIGNAL_H if the header is available.

Added a check in configure that tests if the sig_atomic_t type is
available, defining HAVE_SIG_ATOMIC_T if it is available. Providing
a suitable default in setup_once.h if not available.

Added a check in configure that tests if the sig_atomic_t type is
already defined as volatile, defining HAVE_SIG_ATOMIC_T_VOLATILE
if it is available and already defined as volatile.