libvirt: 6.3.0 -> 6.6.0

Also upgrades `python3Packages.libvirt`
and patches the `rpcgen` tool from Apple's `developer_cmds` package.

pkgs/os-specific/darwin/apple-source-releases/developer_cmds/default.nix

@@ -1,11 +1,18 @@
-{ stdenv, appleDerivation, xcbuildHook }:
+{ stdenv, appleDerivation, xcbuildHook, llvmPackages }:
 
 appleDerivation {
   nativeBuildInputs = [ xcbuildHook ];
 
-  patchPhase = ''
+  patches = [
+    # The following copied from
+    # https://github.com/Homebrew/homebrew-core/commit/712ed3e948868e17f96b7e59972b5f45d4faf688
+    # is needed to build libvirt.
+    ./rpcgen-support-hyper-and-quad-types.patch
+  ];
+
+  postPatch = ''
     substituteInPlace rpcgen/rpc_main.c \
-      --replace "/usr/bin/cpp" "${stdenv.cc}/bin/cpp"
+      --replace "/usr/bin/cpp" "${llvmPackages.clang-unwrapped}/bin/clang-cpp"
   '';
 
   # temporary install phase until xcodebuild has "install" support