[clang] Heap-allocated volatile variables are diagnosed as volatile temporaries

See https://godbolt.org/z/r1s5ds5v5
```c++
constexpr int foo() {
for (int i = 0; i != 10; ++i) {
auto *k = new volatile int{0};

int *p = (int *)k;
*p = 10;
delete k;
}
return 1;
}
static_assert(foo() == 1);
```

```console
:11:15: error: static assertion expression is not an integral constant expression
11 | static_assert(foo() == 1);
| ^~~~~~~~~~
:6:8: note: assignment to volatile temporary is not allowed in a constant expression
6 | *p = 10;
| ^
:11:15: note: in call to 'foo()'
11 | static_assert(foo() == 1);
| ^~~~~
note: volatile temporary created here
```

It's not a temporary though and the source location for the "created here" note is invalid.

Start by reproducing the constexpr example from the issue, using the linked Godbolt case or the shown static_assert. Trace Clang's diagnostic for the assignment through the constant-expression evaluation path; done means the heap-allocated volatile variable is not called a temporary and the creation note points to a valid source location.

Written by the indexing model from the issue text.