[llvm] [Support] Import SipHash c reference implementation. (PR #94393)

[Ahmed Bougacha via llvm-commits]

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@@ -0,0 +1,126 @@
+# SipHash
+
+[![License:
+CC0-1.0](https://licensebuttons.net/l/zero/1.0/80x15.png)](http://creativecommons.org/publicdomain/zero/1.0/)
+
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
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ahmedbougacha wrote:

Yes, I added it only because the text at the end was the only mention of the license I had found.  Happy to remove it!

https://github.com/llvm/llvm-project/pull/94393