[clang] [clang][NFC][diagnostics] Remove several uses of `getCustomDiagID()` (PR #172532)

[Dave Bartolomeo via cfe-commits]

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@@ -1043,6 +1045,36 @@ def warn_npot_ms_struct : Warning<
 def err_itanium_layout_unimplemented : Error<
   "Itanium-compatible layout for the Microsoft C++ ABI is not yet supported">;
 
+// Unsupported features in name mangling
+def err_unsupported_itanium_mangling
+    : Error<"cannot yet mangle "
+            "%enum_select<UnsupportedItaniumManglingKind>"
+            "{%FixedPointLiteral{fixed point literal}"
+            "|%DependentNeonVector{dependent neon vector type}"
+            "|%DependentFixedLengthSVEVector{dependent fixed-length SVE vector "
+            "type}"
+            "|%DependentFixedLengthRVVVectorType{dependent fixed-length RVV "
+            "vector type}"
+            "|%TernaryWithOmittedMiddleOperand{?: operator with omitted middle "
+            "operand}"
+            "|%OpenACCAsteriskSizeExpr{OpenACC Asterisk Size expression}"
+            "|%UnnamedUnionNTTP{unnamed union non-type template parameter}"
+            "|%RequiresExprWithSubstitutionFailure{requires-expression "
+            "containing a substitution failure}"
+            "}0 yet">;
+
+def err_unsupported_itanium_expr_mangling
+    : Error<"cannot yet mangle %0 expression">;
+
+def err_ms_mangle_number_overflow
+    : Error<"mangling number exceeds limit (65535)">;
+def err_ms_mangle_unsupported_with_detail
+    : Error<"cannot mangle this %0 %1 yet">;
+def err_ms_mangle_unsupported : Error<"cannot mangle this %0 yet">;
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dbartol wrote:

Agreed, but let's do that as a follow-up.

https://github.com/llvm/llvm-project/pull/172532