[clang] [llvm] [RISCV] Add support for new unprivileged extensions defined in profiles spec (PR #77458)

[Philip Reames via cfe-commits]

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@@ -96,6 +96,8 @@ on support follow.
      ``Svnapot``      Assembly Support
      ``Svpbmt``       Supported
      ``V``            Supported
+     ``Za128rs``      Supported
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preames wrote:

I think these may warrant an explanatory note after the table.  See what we do for e.g. zicntr.  Something which says these are defined by the profile specification seems like a useful breadcrumb.  

https://github.com/llvm/llvm-project/pull/77458