fix: add libxml 2.11.6 for builds under PHP 8.1

pkgs/libxml2/2.11.nix

@@ -0,0 +1,73 @@
+{
+  stdenv,
+  lib,
+  fetchurl,
+  pkg-config,
+  autoreconfHook,
+  findXMLCatalogs,
+  libiconv,
+  icuSupport ? false,
+  icu,
+}:
+
+stdenv.mkDerivation (finalAttrs: {
+  pname = "libxml2";
+  version = "2.11.6";
+
+  outputs = [
+    "bin"
+    "dev"
+    "out"
+  ];
+  outputMan = "bin";
+
+  src = fetchurl {
+    url = "mirror://gnome/sources/libxml2/${lib.versions.majorMinor finalAttrs.version}/libxml2-${finalAttrs.version}.tar.xz";
+    hash = "sha256-yQ7udQZ2Srvge7YWuC2kUlKWCYFa7+9CPWbvCA6wwwA=";
+  };
+
+  strictDeps = true;
+
+  nativeBuildInputs = [
+    pkg-config
+    autoreconfHook
+  ];
+
+  propagatedBuildInputs = [
+    findXMLCatalogs
+  ] ++ lib.optionals stdenv.isDarwin [ libiconv ] ++ lib.optionals icuSupport [ icu ];
+
+  configureFlags = [
+    "--exec-prefix=${placeholder "dev"}"
+    (lib.withFeature icuSupport "icu")
+    "--without-python"
+  ];
+
+  enableParallelBuilding = true;
+
+  doCheck = (stdenv.hostPlatform == stdenv.buildPlatform) && stdenv.hostPlatform.libc != "musl";
+  preCheck = lib.optional stdenv.isDarwin ''
+    export DYLD_LIBRARY_PATH="$PWD/.libs:$DYLD_LIBRARY_PATH"
+  '';
+
+  preConfigure = lib.optionalString (lib.versionAtLeast stdenv.hostPlatform.darwinMinVersion "11") ''
+    MACOSX_DEPLOYMENT_TARGET=10.16
+  '';
+
+  postFixup = ''
+    moveToOutput bin/xml2-config "$dev"
+    moveToOutput lib/xml2Conf.sh "$dev"
+  '';
+
+  meta = with lib; {
+    homepage = "https://gitlab.gnome.org/GNOME/libxml2";
+    description = "XML parsing library for C";
+    license = licenses.mit;
+    platforms = platforms.all;
+    maintainers = with maintainers; [
+      eelco
+      jtojnar
+    ];
+    pkgConfigModules = [ "libxml-2.0" ];
+  };
+})

pkgs/phps.nix

@@ -9,15 +9,19 @@ let
   packageOverrides = import ./package-overrides.nix prev;
 
   libxml2_12 = prev.callPackage ./libxml2/2.12.nix { };
+  libxml2_11 = prev.callPackage ./libxml2/2.11.nix { };
 
   _mkArgs =
     args:
 
     let
       libxml2 =
-        if prev.lib.versionAtLeast args.version "8.1"
-        then prev.libxml2
-        else libxml2_12;
+        if prev.lib.versionAtLeast args.version "8.1" then
+          prev.libxml2
+        else if prev.lib.versionAtLeast args.version "8.0" then
+          libxml2_11
+        else
+          libxml2_12;
 
       # Use a consistent libxml2 version.
       libxslt = prev.libxslt.override { inherit libxml2; };