[llvm] [bazel] Use zstd from the BCR (PR #169146)

[Keith Smiley via llvm-commits]

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@@ -34,6 +33,8 @@ use_repo(
     "vulkan_sdk",
 )
 
+bazel_dep(name = "zstd", version = "1.5.7", repo_name = "llvm_zstd")
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keith wrote:

i just moved it back to reduce confusion, especially since ones like protobuf can be both

https://github.com/llvm/llvm-project/pull/169146