[libc] [llvm] [libc] Add memcmp / bcmp fuzzers (PR #77741)

[Jordan Rupprecht via llvm-commits]

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rupprecht wrote:

Just noticed this file and couldn't quite figure out what its use is. It looks like maybe it's an artifact of running the fuzz test and forgetting to exclude it from the commit. Is it needed for anything, or should we remove it?

https://github.com/llvm/llvm-project/pull/77741