[Bugfix] Fix __syncwarp on ROCM

[zhewenl]

Purpose

We are seeing failure on AMD due to __syncwarp is exclusively on CUDA but not on HIP

__vllm_cpp_lib_hipify_gen__/out/csrc/cache_kernels.hip:541:3: error: use of undeclared identifier '__syncwarp'; did you mean '__sync_swap'?
  541 |   __syncwarp();
      |   ^~~~~~~~~~
      |   __sync_swap

Test Plan

CI

[simon-mo]

Ok given this fix amd build. Without this op the accuracy will drop in nvidia

[mxz297]

AMD gpu does not support __syncwarp. So to have AMD properly support this, the first thing to try would be __syncthreads, but it would be better to be done under the context of actual adding dsv32 support on AMD. So, this fix at the moment should be good.

[zhewenl]

checking the failing CIs:

• V1 test others is broken on trunk I think: https://app.hex.tech/533fe68e-dcd8-4a52-a101-aefba762f581/app/vLLM-CI-030kdEgDv6lSlh1UPYOkWP/latest
• Kernel Mamba is also broken on the original PR: https://buildkite.com/vllm/ci/builds/32924

@simon-mo could you help force merge this PR? thanks!

[HAIAI]

It is fine for temporary.