coordgenlibs: fix build with LLVM 21

pkgs/by-name/co/coordgenlibs/package.nix

@@ -1,5 +1,6 @@
 {
   fetchFromGitHub,
+  fetchpatch,
   lib,
   stdenv,
   boost,
@@ -19,6 +20,14 @@ stdenv.mkDerivation (finalAttrs: {
     hash = "sha256-casFPNbPv9mkKpzfBENW7INClypuCO1L7clLGBXvSvI=";
   };
 
+  patches = [
+    (fetchpatch {
+      name = "coordgenlibs-fix-unused-but-set-variable.patch";
+      url = "https://github.com/schrodinger/coordgenlibs/commit/6a1485643feb71c6d609d263f28751004c733cf7.patch";
+      hash = "sha256-x34v+XumVip43LYb4bEkdqPFcTRTeC/zsRuQjnrh2zw=";
+    })
+  ];
+
   nativeBuildInputs = [ cmake ];
   buildInputs = [
     boost
@@ -38,6 +47,9 @@ stdenv.mkDerivation (finalAttrs: {
 
   doCheck = true;
 
+  # Fix the build with Clang 20.
+  env.NIX_CFLAGS_COMPILE = lib.optionalString stdenv.cc.isClang "-Wno-error=deprecated-literal-operator";
+
   meta = with lib; {
     description = "Schrodinger-developed 2D Coordinate Generation";
     homepage = "https://github.com/schrodinger/coordgenlibs";