[clang] [clang] deprecate frelaxed-template-template-args, make it on by default (PR #89807)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

Also needs a release note, entry into breaking changes, and a post on mailing list or whatever for the 'breaking change' subscribers to pay attention to.

https://github.com/llvm/llvm-project/pull/89807