[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]

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

To be clear, it's not a "pack-index-specifier" even in C++26: it doesn't match the grammar because there's no constant-expression, and the constant-expression is not optional in the pack-index-specifier grammar.

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