lib: add getgrouplist() for Solaris

Of course Solaris doesn't have getgrouplist()...

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/configure.ac b/configure.ac
index 747a0c6..3003e62 100755
--- a/configure.ac
+++ b/configure.ac
@@ -792,7 +792,7 @@
 	strtol strtoul strlcat strlcpy \
 	daemon snprintf vsnprintf \
 	if_nametoindex if_indextoname getifaddrs \
-	uname fcntl])
+	uname fcntl getgrouplist])
 
 AC_CHECK_FUNCS(setproctitle, ,
   [AC_CHECK_LIB(util, setproctitle,