postgresql: Fix build with libxml2 2.12

libxml 2.12.0 made the error argument of xmlStructuredErrorFunc const
resulting in -Wincompatible-function-pointer-types error with CLang 16 and GCC 14.
https://gitlab.gnome.org/GNOME/libxml2/-/commit/61034116d0a3c8b295c6137956adc3ae55720711

pkgs/servers/sql/postgresql/default.nix

@@ -109,6 +109,17 @@ let
       ./patches/specify_pkglibdir_at_runtime.patch
       ./patches/findstring.patch
 
+      # Fix build with libxml2 2.12.0 and -Wincompatible-function-pointer-types
+      (if atLeast "16" then
+        # https://www.postgresql.org/message-id/CACpMh%2BDMZVHM%2BiDSyqdcpK8sr7jd_HxxLJRNvGTzcLBE0W07QA%40mail.gmail.com
+        fetchurl {
+          url = "https://www.postgresql.org/message-id/attachment/152769/v1-0001-Make-PostgreSQL-work-with-newer-version-of-libxml.patch";
+          hash = "sha256-1j5mtG++hFmYwfS98PdN1SmNI4T86q4FXvKLz2VeJyg=";
+        }
+      else
+        ./patches/libxml2.12-15.patch
+      )
+
       (substituteAll {
         src = ./locale-binary-path.patch;
         locale = "${if stdenv.isDarwin then darwin.adv_cmds else lib.getBin stdenv.cc.libc}/bin/locale";

pkgs/servers/sql/postgresql/patches/libxml2.12-15.patch

@@ -0,0 +1,22 @@
+diff --git a/src/backend/utils/adt/xml.c b/src/backend/utils/adt/xml.c
+index 6411f56b998..0eb39fcfc26 100644
+--- a/src/backend/utils/adt/xml.c
++++ b/src/backend/utils/adt/xml.c
+@@ -119,7 +119,7 @@ struct PgXmlErrorContext
+ 
+ static xmlParserInputPtr xmlPgEntityLoader(const char *URL, const char *ID,
+ 										   xmlParserCtxtPtr ctxt);
+-static void xml_errorHandler(void *data, xmlErrorPtr error);
++static void xml_errorHandler(void *data, const xmlError *error);
+ static void xml_ereport_by_code(int level, int sqlcode,
+ 								const char *msg, int errcode);
+ static void chopStringInfoNewlines(StringInfo str);
+@@ -1749,7 +1749,7 @@ xml_ereport(PgXmlErrorContext *errcxt, int level, int sqlcode, const char *msg)
+  * Error handler for libxml errors and warnings
+  */
+ static void
+-xml_errorHandler(void *data, xmlErrorPtr error)
++xml_errorHandler(void *data, const xmlError *error)
+ {
+ 	PgXmlErrorContext *xmlerrcxt = (PgXmlErrorContext *) data;
+ 	xmlParserCtxtPtr ctxt = (xmlParserCtxtPtr) error->ctxt;