[clang] [clang] Fix side effects resolving overloads of builtin functions (#138651) (PR #154034)

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comex wrote:

Updated.  Aside from adding a release note, I also discovered some related issues that are fixed by adding a `SFINAETrap` in addition to the `EnterExpressionEvaluationContext`.  See the added test in `non-trivial-c-union.m` (the `__builtin_addressof` call previously yielded a compile error), and the modified test in `builtin-get-vtable-pointer.cpp` (one of the calls previously yielded two copies of the same compile error; now it only yields one).

https://github.com/llvm/llvm-project/pull/154034