Cygwin doesn't have setgroups() so probe for the function in configure

and don't try to call it if it doesn't exist.

clientserver.c

@@ -287,6 +287,7 @@ static int rsync_module(int fd, int i)
 	}
 
 	if (am_root) {
+#ifdef HAVE_SETGROUPS
 		/* Get rid of any supplementary groups this process
 		 * might have inheristed. */
 		if (setgroups(0, NULL)) {
@@ -294,6 +295,7 @@ static int rsync_module(int fd, int i)
 			io_printf(fd, "@ERROR: setgroups failed\n");
 			return -1;
 		}
+#endif
 
 		/* XXXX: You could argue that if the daemon is started
 		 * by a non-root user and they explicitly specify a

configure.in

@@ -351,7 +351,7 @@ AC_FUNC_UTIME_NULL
 AC_CHECK_FUNCS(waitpid wait4 getcwd strdup strerror chown chmod mknod)
 AC_CHECK_FUNCS(fchmod fstat strchr readlink link utime utimes strftime)
 AC_CHECK_FUNCS(memmove lchown vsnprintf snprintf asprintf setsid glob strpbrk)
-AC_CHECK_FUNCS(strlcat strlcpy mtrace mallinfo)
+AC_CHECK_FUNCS(strlcat strlcpy mtrace mallinfo setgroups)
 
 AC_CACHE_CHECK([for working socketpair],rsync_cv_HAVE_SOCKETPAIR,[
 AC_TRY_RUN([