[clang] move -Wcast-function-type under -Wextra

[nickdesaulniers]

via #74617, I was looking into why I observe this diagnostic with gcc but not clang. It looks like our project (llvmlibc) builds with -Wextra but not -Wcast-function-type. GCC 8 added support for that flag, and did so under -Wextra.

[llvmbot]

Hi!

This issue may be a good introductory issue for people new to working on LLVM. If you would like to work on this issue, your first steps are:

1. In the comments of the issue, request for it to be assigned to you.
2. Fix the issue locally.
3. Run the test suite locally. Remember that the subdirectories under test/ create fine-grained testing targets, so you can e.g. use make check-clang-ast to only run Clang's AST tests.
4. Create a Git commit.
5. Run git clang-format HEAD~1 to format your changes.
6. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation.

If you have any further questions about this issue, don't hesitate to ask via a comment in the thread below.

[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Nick Desaulniers (nickdesaulniers)

via https://github.com//issues/74617, I was looking into why I observe this diagnostic with gcc but not clang. It looks like our project (llvmlibc) builds with -Wextra but not -Wcast-function-type. GCC 8 added support for that flag, and did so under -Wextra.

[Abhinkop]

Can I pick up this issue?

[nickdesaulniers]

@Abhinkop sure. I'd expect you to change clang/include/clang/Basic/DiagnosticGroups.td's record of Extra to include CastFunctionType, then update the test for -Wcast-function-type to add an additional RUN with just -Wextra and produce the same diagnostics.

[Abhinkop]

@nickdesaulniers Here is the pull request #77178.