[clang] Check for mutability better (PR #127843)

[Hans Wennborg via cfe-commits]

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@@ -13440,6 +13440,23 @@ bool Sema::GloballyUniqueObjectMightBeAccidentallyDuplicated(
   return true;
 }
 
+// Determine whether the object seems mutable for the purpose of diagnosing
+// possible unique object duplication, i.e. non-const-qualified, and
+// not an always-constant type like a function.
+// Not perfect: doesn't account for mutable members, for example, or
+// elements of container types.
+// For nested pointers, any individual level being non-const is sufficient.
+bool looksMutable(QualType T, const ASTContext &Ctx) {
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zmodem wrote:

nit: make it `static` since it's local to this file

https://github.com/llvm/llvm-project/pull/127843