[clang] [Clang] Add '-Warray-compare' flag for C++ below version 20 (PR #118031)

[Erich Keane via cfe-commits]

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@@ -10264,6 +10264,10 @@ def warn_depr_array_comparison : Warning<
   "to compare array addresses, use unary '+' to decay operands to pointers">,
   InGroup<DeprecatedArrayCompare>;
 
+def warn_array_comparison : Warning<
+  "comparison between two arrays compare their addresses and will be deprecated in c++20; "
+  "to compare array addresses, use unary '+' to decay operands to pointers">;
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erichkeane wrote:

He means to inline the diagnostic group, so instead of `InGroup<SomeName>` you can do: `InGroup<DiagnosticGroup<"Group name">>`

(I think you might have to grep here for proper spelling).

https://github.com/llvm/llvm-project/pull/118031