libmilter: fix build w/glibc-2.30

Using RES_USE_INET6 is deprecated and has been removed by glibc 2.30[1].
Instead, there's now a function `gethostbyname2(3)` which takes the
address family as second argument to force IPv6 resolution[2].

[1] https://sourceware.org/ml/libc-alpha/2019-08/msg00029.html
[2] https://linux.die.net/man/3/gethostbyname2

pkgs/development/libraries/libmilter/default.nix

@@ -31,7 +31,7 @@ stdenv.mkDerivation rec {
     sh Build -f ./a.m4
   '';
 
-  patches = [ ./install.patch ./sharedlib.patch ];
+  patches = [ ./install.patch ./sharedlib.patch ./glibc-2.30.patch ];
 
   nativeBuildInputs = [ m4 ];