[clang] __STDC_NO_THREADS__ is no longer necessary for VS 2022 17.8

[latal-1]

Starting with VS 2022 17.8, the __STDC_NO_THREADS__ is no longer relevant due to the addition of thread library

Сommit with the addition of a macro bbc690c

[AaronBallman]

17.7: defines __STDC_NO_THREADS__ does not supply <threads.h>
17.8: does not define __STDC_NO_THREADS__ does not supply <threads.h>
17.9: does not define __STDC_NO_THREADS__, does supply <threads.h>

https://godbolt.org/z/f8san8Ebe

Part of the challenge is that the CRT is defined at runtime rather than at compile time, so it's hard to know whether the 17.8 behavior is because of an old CRT or not.

[AaronBallman]

This seems like a reasonably good first issue.

In addVisualCDefines() in clang/lib/Basic/Targets/OSTargets.cpp, guard the call to Builder.defineMacro("__STDC_NO_THREADS__"); on the version of Visual Studio we're aiming to be compatible with. You'll likely need to add a new enumeration to MSVCMajorVersion to represent MSVC 17.8 (1938 would be the value for the enumeration).

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: None (latal-1)

Starting with [VS 2022 17.8](https://learn.microsoft.com/en-us/visualstudio/releases/2022/release-notes-v17.8), the `__STDC_NO_THREADS__` is no longer relevant due to the addition of thread library

Сommit with the addition of a macro bbc690c

[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. Check that no other contributor has already been assigned to this issue. If you believe that no one is actually working on it despite an assignment, ping the person. After one week without a response, the assignee may be changed.
2. In the comments of this issue, request for it to be assigned to you, or just create a pull request after following the steps below. Mention this issue in the description of the pull request.
3. Fix the issue locally.
4. 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.
5. Create a Git commit.
6. Run git clang-format HEAD~1 to format your changes.
7. Open a pull request to the upstream repository on GitHub. Detailed instructions can be found in GitHub's documentation. Mention this issue in the description of the pull request.

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