[clang] [libcxx] [llvm] [Clang] Add warnings when mixing different charN_t types (PR #138708)

[Aaron Ballman via llvm-commits]

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@@ -111,6 +111,7 @@ def EnumConversion : DiagGroup<"enum-conversion",
                                 ImplicitEnumEnumCast,
                                 EnumFloatConversion,
                                 EnumCompareConditional]>;
+def ImplicitUnicodeConversion : DiagGroup<"implicit-unicode-conversion">;
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AaronBallman wrote:

Given that we already have `def StringConversion : DiagGroup<"string-conversion">;` I think `character-conversion` may be a reasonable name. (I'm not sold on "suspicious" being a good group name.)

Should we add this new group to `-Wconversion`?

https://github.com/llvm/llvm-project/pull/138708