libmypaint: fix build (#424557)

`dev` output unchanged (verified by `diffoscope`).

`out` output still contains all the translation files,
with no obvious encoding issues i spotted. Slight
deviations in the metadata, but should be fine.

Fixing the build with modern gettext requires replacing the obsolete glib gettext.
Fixing the build with modern autoconf requires making IT_PROG_INTLTOOL
unconditional, hence the indent changes in the patch.

pkgs/by-name/li/libmypaint/0001-configure-use-regular-GETTEXT-unconditionally.patch

@@ -0,0 +1,37 @@
+From dd663ee7bf6a2ff7dd47fc360ac7cd44c83039d0 Mon Sep 17 00:00:00 2001
+From: Grimmauld <Grimmauld@grimmauld.de>
+Date: Sat, 12 Jul 2025 12:46:58 +0200
+Subject: [PATCH] configure: use regular GETTEXT unconditionally
+
+Modern autoconf breaks when `IT_PROG_INTLTOOL` is conditional [1].
+
+`glib` gettext is obsolete and broken, so switch to regular gettext instead.
+This also needs to be unconditional.
+
+To achieve unconditional directives, indentation needs to be removed
+as indentation is part of the syntax.
+
+[1] https://github.com/mypaint/libmypaint/issues/178
+---
+ configure.ac | 5 +++--
+ 1 file changed, 3 insertions(+), 2 deletions(-)
+
+diff --git a/configure.ac b/configure.ac
+index 416d9fe..9479db9 100644
+--- a/configure.ac
++++ b/configure.ac
+@@ -248,8 +248,9 @@ if test "x$enable_i18n" != "xno"; then
+   AC_DEFINE_UNQUOTED(GETTEXT_PACKAGE, "$GETTEXT_PACKAGE",
+                      [The prefix for our gettext translation domains.])
+   AC_SUBST(GETTEXT_PACKAGE)
+-  IT_PROG_INTLTOOL
+-  AM_GLIB_GNU_GETTEXT
++IT_PROG_INTLTOOL
++AM_GNU_GETTEXT([external])
++AM_GNU_GETTEXT_VERSION([0.21])
+ 
+   dnl Debian: stdlib
+   dnl Windows, and OSX: -lintl
+-- 
+2.49.0
+

pkgs/by-name/li/libmypaint/package.nix

@@ -1,8 +1,6 @@
 {
   lib,
   stdenv,
-  autoconf,
-  automake,
   fetchFromGitHub,
   glib,
   intltool,
@@ -10,6 +8,8 @@
   libtool,
   pkg-config,
   python3,
+  gettext,
+  autoreconfHook,
 }:
 
 stdenv.mkDerivation rec {
@@ -28,12 +28,17 @@ stdenv.mkDerivation rec {
     sha256 = "1ppgpmnhph9h8ayx9776f79a0bxbdszfw9c6bw7c3ffy2yk40178";
   };
 
+  patches = [
+    # glib gettext macros are broken/obsolete,
+    # so we patch libmypaint to use regular gettext instead.
+    ./0001-configure-use-regular-GETTEXT-unconditionally.patch
+  ];
+
   strictDeps = true;
 
   nativeBuildInputs = [
-    autoconf
-    automake
-    glib # AM_GLIB_GNU_GETTEXT
+    autoreconfHook
+    gettext
     intltool
     libtool
     pkg-config