[clang] [clang][Sema] fix crash on __type_pack_element with dependent packs (GH180307) (PR #180407)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> @mizvekov @ojhunt is checkTemplateArgumentList the right place to catch those pack expansion errors? I am thinking of adding BuiltinTemplateDecl there so it works like alias templates and catches it

Yeah, that looks like the right approach.

https://github.com/llvm/llvm-project/pull/180407