Okay. gnu gettext vendors libxml2. The following patch drops the dependency on gettext for libxml:

diff --git a/pkgs/development/libraries/libxml2/common.nix b/pkgs/development/libraries/libxml2/common.nix
index bc43cfd9d6e3..f16656b0798b 100644
--- a/pkgs/development/libraries/libxml2/common.nix
+++ b/pkgs/development/libraries/libxml2/common.nix
@@ -3,7 +3,9 @@
   darwin,
   lib,
   pkg-config,
-  autoreconfHook,
+  autoconf,
+  automake,
+  libtool,
   python3,
   doxygen,
   ncurses,
@@ -55,7 +57,9 @@ stdenv'.mkDerivation (finalAttrs: {
 
   nativeBuildInputs = [
     pkg-config
-    autoreconfHook
+    autoconf
+    automake
+    libtool
   ]
   ++ lib.optionals pythonSupport [
     doxygen
@@ -112,7 +116,11 @@ stdenv'.mkDerivation (finalAttrs: {
       ln -s cygxml2mod.dll python/.libs/libxml2mod.dll
     '';
 
-  preConfigure = lib.optionalString (lib.versionAtLeast stdenv.hostPlatform.darwinMinVersion "11") ''
+  # Uses `autoreconf -i` instead of autoreconfHook to avoid gettext dependency
+  preConfigure = ''
+    autoreconf -i
+  ''
+  + lib.optionalString (lib.versionAtLeast stdenv.hostPlatform.darwinMinVersion "11") ''
     MACOSX_DEPLOYMENT_TARGET=10.16
   '';
 

However, adding libxml2 to gettext buildInputs (to make it use thedynamic lib) throws obscure splicing errors, and i am not sure where to even start fixing it. I can fix builds, but eval in splicing and stdenv bootstrap is painful. Ideas welcome.

Looks like you can't use fetchFromGitLab in the bootstrap process (like fetchpatch)? With this patch, it evals (I haven't built):

diff --git a/pkgs/development/libraries/libxml2/default.nix b/pkgs/development/libraries/libxml2/default.nix
index 41d2b1f953f0..43df6360ade5 100644
--- a/pkgs/development/libraries/libxml2/default.nix
+++ b/pkgs/development/libraries/libxml2/default.nix
@@ -2,6 +2,7 @@
   lib,
   callPackage,
   fetchFromGitLab,
+  fetchurl,
   fetchpatch,
 }:

@@ -49,14 +50,12 @@ let
         ];
       };
     };
-    libxml2 = callPackage ./common.nix {
+    libxml2 = callPackage ./common.nix rec {
       version = "2.15.1";
-      src = fetchFromGitLab {
-        domain = "gitlab.gnome.org";
-        owner = "GNOME";
-        repo = "libxml2";
-        tag = "v${packages.libxml2.version}";
-        hash = "sha256-FUfYMq5xT2i88JdIw9OtSofraUL3yjsyOVund+mfJKQ=";
+      src = fetchurl {
+        name = "libxml2-${version}-source.tar.gz";
+        url = "https://gitlab.gnome.org/api/v4/projects/GNOME%2Flibxml2/repository/archive.tar.gz?sha=refs/tags/v${packages.libxml2.version}";
+        hash = "sha256-2py4DlRIlD4h1x8379d+whzsNbh8ofHpNAad/QFsTuw=";
       };
       extraMeta = {
         maintainers = with lib.maintainers; [