[clang] [clang] Add covariance tests that make sure we return an error when return value is different in pointer / lvalue ref / rvalue ref (PR #112853)

[Boaz Brickner via cfe-commits]

bricknerb wrote:

> You should write a test in `clang/test/CXX/drs/cwg0xx.cpp`, possibly by moving the test you've written there. While doing that, you should follow the example of other tests in that file, which includes the way `expected` directives are written, and the presence of `// cwg960: NN` comment that describes what our support for CWG960 is. Then you need to run `clang/www/make_cxx_dr_status` script which generated our "C++ DR Status" page in the documentation: https://clang.llvm.org/cxx_dr_status.html

Done.
`clang/www/make_cxx_dr_status` seems to generate a lot of unrelated changes, so perhaps a separate pull request would make sense if we want to update cxx_dr_status.html.

https://github.com/llvm/llvm-project/pull/112853