These tests use an old way to test code in constexpr context. This
changes the code to the idomatic libc++ method.
This is a preparation for #73162.
Side changes
- Updated formatting
- Made some helper functions constexpr
- Some naming improvements
In the C++20 Standard time is no longer section under utilities, but
became its own chapter. This moves the time tests accordingly so their
location matches the current Standard.
Reviewed By: ldionne, #libc
Differential Revision: https://reviews.llvm.org/D122745