[llvm] Document Policy on supporting newer C++ standard in LLVM codebase (PR #156823)

[Nikita Popov via llvm-commits]

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@@ -78,6 +78,12 @@ Each toolchain provides a good reference for what it accepts:
 Additionally, there are compiler comparison tables of supported C++ features on
 `cppreference.com <https://en.cppreference.com/w/cpp/compiler_support/17>`_.
 
+To keep track with the evolution of the standard, newer C++ version can be used
+to build LLVM. However, our support focuses on the minimum supported C++
+version and a very recent standard may not be yet supported, or only using the
----------------
nikic wrote:

```suggestion
version and a very recent standard may not yet be supported, or only using the
```

https://github.com/llvm/llvm-project/pull/156823