[libc] [llvm] [libc] delete hdrgen (PR #117220)

[Nick Desaulniers via llvm-commits]

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@@ -86,16 +86,13 @@ compiler. These tools must all be up-to-date with the libc source.
      -DCMAKE_C_COMPILER=$HOST_C_COMPILER      \
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nickdesaulniers wrote:

4a474332c8f3

https://github.com/llvm/llvm-project/pull/117220