[libcxx-commits] [libcxx] [libc++] Add base for LLVM 19 release notes (PR #78990)

[Mark de Wever via libcxx-commits]

https://github.com/mordante commented:

I didn't add this originally with the removal of 17. The documentation fails to build due to an referenced `.rst` file. Either we could wait until after branching or temporary rename the fix, maybe `.txt`.

https://github.com/llvm/llvm-project/pull/78990