[clang] [llvm] Remove mmx 3dnow (PR #96246)

[Simon Pilgrim via llvm-commits]

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@@ -7,151 +7,16 @@
  *===-----------------------------------------------------------------------===
  */
 
+// 3dNow intrinsics are no longer supported, and this header remains only as a
+// stub for users who were including it to get to _m_prefetch or
+// _m_prefetchw. Such uses should prefer x86intrin.h.
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RKSimon wrote:

How best can we add a deprecation warning to builds for people who are doing this?

https://github.com/llvm/llvm-project/pull/96246