[clang] [Clang] Allow explicit member specialization to differ from template declaration wrt constexpr (PR #145272)

[Erich Keane via cfe-commits]

https://github.com/erichkeane commented:

it would be great to track down the history of this (https://github.com/cplusplus/draft) to see what changed around this, in case there is more we have to think about.  We ALSO might be able to move the tests into the CWG issues section (though likely, not for functions!).

Also-also: this needs a release note.

https://github.com/llvm/llvm-project/pull/145272