configure: test for IPV6_TCLASS.

* Haiku does not define IPV6_TCLASS.

Author: jessicah

Network/Socket/Posix/Cmsg.hsc

@@ -64,7 +64,11 @@ pattern CmsgIdIPv4TOS = CmsgId (#const IPPROTO_IP) (#const IP_TOS)
 
 -- | The identifier for 'IPv6TClass'.
 pattern CmsgIdIPv6TClass :: CmsgId
+#if defined(IPV6_TCLASS)
 pattern CmsgIdIPv6TClass = CmsgId (#const IPPROTO_IPV6) (#const IPV6_TCLASS)
+#else
+pattern CmsgIdIPv6TClass = CmsgId (-1) (-1)
+#endif
 
 -- | The identifier for 'IPv4PktInfo'.
 pattern CmsgIdIPv4PktInfo :: CmsgId

configure.ac

@@ -83,7 +83,7 @@ AC_CHECK_FUNCS([gai_strerror gethostent accept4])
 AC_CHECK_FUNCS([getpeereid])
 
 AC_CHECK_DECLS([AI_ADDRCONFIG, AI_ALL, AI_NUMERICSERV, AI_V4MAPPED])
-AC_CHECK_DECLS([IPV6_V6ONLY])
+AC_CHECK_DECLS([IPV6_V6ONLY, IPV6_TCLASS])
 AC_CHECK_DECLS([IPPROTO_IP, IPPROTO_TCP, IPPROTO_IPV6])
 AC_CHECK_DECLS([SO_PEERCRED])