Make some of the headers used by the KAME getaddrinfo implementation

be conditional -- they are missing on e.g. Solaris.  Not sure if this
will fix it.

configure.in

@@ -343,7 +343,7 @@ AC_HEADER_SYS_WAIT
 AC_CHECK_HEADERS(sys/fcntl.h sys/select.h fcntl.h sys/time.h sys/unistd.h unistd.h utime.h grp.h)
 AC_CHECK_HEADERS(compat.h sys/param.h ctype.h sys/wait.h sys/ioctl.h)
 AC_CHECK_HEADERS(sys/filio.h string.h stdlib.h sys/socket.h sys/mode.h)
-AC_CHECK_HEADERS(glob.h alloca.h mcheck.h)
+AC_CHECK_HEADERS(glob.h alloca.h mcheck.h sys/sysctl.h arpa/inet.h arpa/nameser.h)
 
 AC_CHECK_SIZEOF(int)
 AC_CHECK_SIZEOF(long)