Changes to compile under gnu-win32, from Marcus Daniels:

Changes to compile under gnu-win32, from Marcus Daniels:
* configure.in: When sys/un.h exists, define HAVE_UNIX_DOMAIN_SOCKETS
to indicate that Unix domain sockets will work.
Check for socketpair, getgroups, setwent, pause, and tzset
(cygwin currently lacks these them).
Check for sethostent endhostent getnetent setnetent endnetent
getprotoent endprotoent getservent endservent getnetbyaddr
getnetbyname inet_lnaof inet_makeaddr inet_netof (cygwin currently
lacks them).  In the case of cygwin, temporarily prefix these
functions with "cygwin32_", the way that netdb.h does.
Don't define HAVE_REGCOMP unless both regcomp and regex.h are
available (cygwin b18 came distributed without a working regex.h
file).
* acconfig.h (HAVE_UNIX_DOMAIN_SOCKETS): Add this.
* configure: Regenerated.