[PATCH] D51762: First part of the <chrono> calendar stuff

[Eric Fiselier via Phabricator via cfe-commits]

EricWF requested changes to this revision.
EricWF added a comment.
This revision now requires changes to proceed.

Have you run `git clang-format` over this change set?

The blocking issues I see are:

- The literal's need to be guarded against older clang dialects. So do their tests.
- There are a bunch of tests with meaningless `XFAIL` directives in them. They need to be removed.



================
Comment at: include/chrono:2667
+#if _LIBCPP_STD_VER > 17
+    constexpr chrono::day operator ""d(unsigned long long __d) noexcept
+    {
----------------
Including this file with Clang 6.0 in C++2a mode causes a compile error because of "-Wreserved-user-defined-literal". We need to wrap this block with:

```
#if defined(__clang__)
#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Wreserved-user-defined-literal"
#endif
    [...]
#if defined(__clang__)
#pragma clang diagnostic pop
#endif
```


https://reviews.llvm.org/D51762