libodfgen: fix build with gcc15

- add patch that adds `#include <cstdint>` to `OdfGenerator.cxx`,
based on upstream commit that is not included in tagged versions:
https://sourceforge.net/p/libwpd/libodfgen/ci/4da0b148def5b40ee60d4cd79762c0f158d64cc7/

Fixes build failure with gcc15:
```
OdfGenerator.cxx:53:9: error: 'uint8_t' was not declared in this scope
   53 |         uint8_t first;
      |         ^~~~~~~
OdfGenerator.cxx:45:1: note: 'uint8_t' is defined in header '<cstdint>';
this is probably fixable by adding '#include <cstdint>'
   44 | #include "GraphicFunctions.hxx"
  +++ |+#include <cstdint>
   45 | #include "InternalHandler.hxx"
OdfGenerator.cxx:57:17: error: 'first' was not declared in this scope
   57 |                 first = 0;
      |                 ^~~~~
```

pkgs/by-name/li/libodfgen/libodfgen-add-include-cstdint-gcc15.patch

@@ -0,0 +1,12 @@
+diff --git a/src/OdfGenerator.cxx b/src/OdfGenerator.cxx
+index adf176b0a4..79de4dd2b7 100644
+--- a/src/OdfGenerator.cxx
++++ b/src/OdfGenerator.cxx
+@@ -33,6 +33,7 @@
+ #include <math.h>
+
+ #include <cctype>
++#include <cstdint>
+ #include <limits>
+ #include <string>
+ #include <stack>

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

@@ -20,6 +20,12 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-Mj5JH5VsjKKrsSyZjjUGcJMKMjF7+WYrBhXdSzkiuDE=";
   };
 
+  patches = [
+    # Fix build with gcc15, based on:
+    # https://sourceforge.net/p/libwpd/libodfgen/ci/4da0b148def5b40ee60d4cd79762c0f158d64cc7/
+    ./libodfgen-add-include-cstdint-gcc15.patch
+  ];
+
   nativeBuildInputs = [ pkg-config ];
   buildInputs = [
     boost