[clang] [Clang][Parser] Make 'T...[N]' within a function parameter a valid pack expansion prior to C++2c (PR #116332)

[Eli Friedman via cfe-commits]

================
@@ -58,8 +58,9 @@ void b(T[] ...);
 
 template<typename T>
 void c(T ... []); // expected-error {{expected expression}} \
----------------
efriedma-quic wrote:

Consider:

```
template<typename ...T>void c(T ... []);
```

Earlier versions of clang consider this valid: it's a function that takes pointers to each type T as arguments (after decay).  So the "expected expression" error is wrong.

https://github.com/llvm/llvm-project/pull/116332