Clang++ crashes when instantiating a particular template class with a static constexpr data member.

This code makes clang++ to crash:

```c++
template
struct S {
static constexpr char c{};
static constexpr decltype(&c) p = nullptr;
};

auto f() {
return S::p;
}
```

GCC and MSVC have no issue to compile the code.

https://godbolt.org/z/edr4h4v99

If instead of being deduced, the type of `S::p` or the return type of `f` is explicitly given (`const char*`), then compilation succeeds.

Start by compiling the reduced C++ reproducer with clang++ from the linked Compiler Explorer example and compare it with the versions that explicitly specify the pointer or return type. Use the crash location and template-instantiation path to identify the affected compiler subsystem. Done means the reproducer no longer crashes and coverage prevents this regression.

Written by the indexing model from the issue text.