[clang] [Clang][Sema] Disable checking invalid template id in initializer of primary variable template `std::format_kind` with libstdc++ (PR #139560)

[via cfe-commits]

cor3ntin wrote:

I think we should
 - 1/ Land this patch as is
 - 2/ Extract the parsing of `__GLIBCXX__` in a separate function
 - 3/ have a function, probably in Preprocessor (so that it is available from Sema and Parser) such as `IsLibStdCxxBefore(_version_)` that let us do these checks uniformly and are easy to grep for. Ditto for libc++.

I don't have time at the moment but it would be a useful improvement :)

https://github.com/llvm/llvm-project/pull/139560