[CUDA][HIP] Externalize kernels in anonymous name space

kernels in anonymous name space needs to have unique name
to avoid duplicate symbols.

Fixes: https://github.com/llvm/llvm-project/issues/54560

Reviewed by: Artem Belevich

Differential Revision: https://reviews.llvm.org/D123353

(cherry picked from commit 4ea1d435)