[clang] [Clang][Sema] Diagnose unexpanded packs in the template argument lists of function template specializations (PR #76677)

[Erich Keane via cfe-commits]

erichkeane wrote:

Reverted here: https://github.com/llvm/llvm-project/pull/76876

@sdkrystian : please take a look at the regression that nico pointed out and re-submit with considerations for that.

https://github.com/llvm/llvm-project/pull/76677