ctranslate2: explicitly set nvcc -gencode flags

This fixes a build failure when using cudaPackages_13:
> Unsupported gpu architecture 'compute_53'

Verified builds both with and without `cudaPackages = cudaPackages_13`
override, on x86_64-linux and aarch64-linux

pkgs/by-name/ct/ctranslate2/cuda-arch-gencode-flags.patch

@@ -0,0 +1,11 @@
+--- a/CMakeLists.txt
++++ b/CMakeLists.txt
+@@ -538,8 +538,6 @@
+     list(REMOVE_DUPLICATES CUDA_ARCH_LIST)
+   endif()
+ 
+-  cuda_select_nvcc_arch_flags(ARCH_FLAGS ${CUDA_ARCH_LIST})
+-  list(APPEND CUDA_NVCC_FLAGS ${ARCH_FLAGS})
+   set(CUDA_HOST_COMPILER ${CMAKE_CXX_COMPILER})
+ 
+   # flags for flash attention

pkgs/by-name/ct/ctranslate2/package.nix

@@ -65,6 +65,15 @@ stdenv'.mkDerivation (finalAttrs: {
     hash = "sha256-OuN7GTfzqsALu8Qgx7GNERlyCq3cTxhpZo8UA/yDekw=";
   };
 
+  patches = [
+    # ctranslate2 uses a deprecated cmake FindCUDA cuda_select_nvcc_arch_flags()
+    # function. This function uses a regex that can not match two-digit
+    # capabilities such as 10.0 and 12.1, and it's default "Auto" fallback still
+    # targets compute_53, which CUDA 13 no longer supports, so the patch removes
+    # its arch selection, and we set CUDA_NVCC_FLAGS ourselves below.
+    ./cuda-arch-gencode-flags.patch
+  ];
+
   # Fix CMake 4 compatibility
   postPatch = ''
     substituteInPlace third_party/cpu_features/CMakeLists.txt \
@@ -103,6 +112,9 @@ stdenv'.mkDerivation (finalAttrs: {
     (lib.cmakeBool "WITH_MKL" withMkl)
     (lib.cmakeBool "WITH_HIP" rocmSupport)
   ]
+  ++ lib.optionals withCUDA [
+    (lib.cmakeFeature "CUDA_NVCC_FLAGS" (lib.concatStringsSep ";" cudaPackages.flags.gencode))
+  ]
   ++ lib.optionals rocmSupport [
     (lib.cmakeBool "CMAKE_SKIP_RPATH" true)
     (lib.cmakeFeature "CMAKE_C_COMPILER" "amdclang")