Clean up ggml-cuda.cu warnings when compiling with clang (for ROCM) (#4124)
* ggml-cuda.cu: Clean up warnings when compiling with clang
* ggml-cuda.cu: Move static items into anonymous namespace
* ggml-cuda.cu: Fix use of namespace start macro
* Revert "ggml-cuda.cu: Fix use of namespace start macro"
This reverts commit 26c11490266c096e3e5731e05270a8f73a5b2874.
* Revert "ggml-cuda.cu: Move static items into anonymous namespace"
This reverts commit e29757e0f7535d1ac314300f0324684cc785e06c.