fix(llama-cpp-rocm): wire rocwmma include path for hipcc

rocwmma is header-only and ships no CMake config file, so
find_package(rocwmma) is not available. hipcc/clang also bypass the
nixpkgs cc-wrapper that would normally pick up headers from
buildInputs, so the rocwmma path was unreachable and the build failed
with:

  ggml-cuda/vendors/hip.h: 'rocwmma/rocwmma-version.hpp' file not found

Inject -I<rocwmma>/include via CMAKE_HIP_FLAGS (HIP TUs) and
CMAKE_CXX_FLAGS (C++ TUs that include hip.h transitively).

overlays/unstable/default.nix

@@ -34,9 +34,13 @@ final: prev: {
           channels.unstable.rocmPackages.rocwmma
         ];
 
+        # rocwmma is header-only and ships no CMake config; hipcc/clang
+        # bypass the cc-wrapper, so inject the include path directly.
         cmakeFlags = (prevAttrs.cmakeFlags or [ ]) ++ [
           "-DGGML_HIP_ROCWMMA_FATTN=ON"
           "-DGGML_HIP_GRAPHS=ON"
+          "-DCMAKE_HIP_FLAGS=-I${channels.unstable.rocmPackages.rocwmma}/include"
+          "-DCMAKE_CXX_FLAGS=-I${channels.unstable.rocmPackages.rocwmma}/include"
         ];
       });