[clang] [Clang] Add diagnostic when scoped enumeration requires an explicit conversion for binary operations (PR #152698)

[Yanzuo Liu via cfe-commits]

================
@@ -4401,6 +4401,11 @@ def warn_impcast_different_enum_types : Warning<
 def warn_impcast_int_to_enum : Warning<
   "implicit conversion from %0 to enumeration type %1 is invalid in C++">,
   InGroup<ImplicitIntToEnumCast>, DefaultIgnore;
+
+def note_no_implicit_conversion_for_scoped_enum
+    : Note<"no implicit conversion for scoped enum; consider casting to "
----------------
zwuis wrote:

We can mention `std::to_underlying` in C++23 mode.

https://github.com/llvm/llvm-project/pull/152698