Include netinet6/in6.h (#728)

On some platforms, "netinet6/in6.h" is not included by "netinet/in.h"
and needs to be included separately.

Fix By: Faraz (@farazrbx)

CMakeLists.txt

@@ -207,6 +207,7 @@ CHECK_INCLUDE_FILES (malloc.h              HAVE_MALLOC_H)
 CHECK_INCLUDE_FILES (memory.h              HAVE_MEMORY_H)
 CHECK_INCLUDE_FILES (netdb.h               HAVE_NETDB_H)
 CHECK_INCLUDE_FILES (netinet/in.h          HAVE_NETINET_IN_H)
+CHECK_INCLUDE_FILES (netinet6/in6.h        HAVE_NETINET6_IN6_H)
 # On old MacOS SDK versions, you must include sys/socket.h before net/if.h
 IF (HAVE_SYS_SOCKET_H)
   CHECK_INCLUDE_FILES ("sys/socket.h;net/if.h"  HAVE_NET_IF_H)
@@ -323,6 +324,7 @@ CARES_EXTRAINCLUDE_IFSET (HAVE_NETDB_H        netdb.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_NET_IF_H       net/if.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_IFADDRS_H      ifaddrs.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_NETINET_IN_H   netinet/in.h)
+CARES_EXTRAINCLUDE_IFSET (HAVE_NETINET6_IN6_H netinet6/in6.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_NETINET_TCP_H  netinet/tcp.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_SIGNAL_H       signal.h)
 CARES_EXTRAINCLUDE_IFSET (HAVE_STDLIB_H       stdlib.h)

configure.ac

@@ -436,6 +436,7 @@ AC_CHECK_HEADERS(
        netioapi.h \
        netdb.h \
        netinet/in.h \
+       netinet6/in6.h \
        netinet/tcp.h \
        net/if.h \
        ifaddrs.h \

src/lib/ares_config.h.cmake

@@ -212,6 +212,9 @@
 /* Define to 1 if you have the <netinet/in.h> header file. */
 #cmakedefine HAVE_NETINET_IN_H
 
+/* Define to 1 if you have the <netinet6/in6.h> header file. */
+#cmakedefine HAVE_NETINET6_IN6_H
+
 /* Define to 1 if you have the <netinet/tcp.h> header file. */
 #cmakedefine HAVE_NETINET_TCP_H
 

src/lib/ares_ipv6.h

@@ -27,6 +27,10 @@
 #ifndef ARES_IPV6_H
 #define ARES_IPV6_H
 
+#ifdef HAVE_NETINET6_IN6_H
+#  include <netinet6/in6.h>
+#endif
+
 #ifndef HAVE_PF_INET6
 #  define PF_INET6 AF_INET6
 #endif