When trying to express a time before the epoch (e.g. "one nanosecond before 00:01:40 on 1900-01-01") the date would be shown as: 1900-01-01 00:01:39.-00000001 After this patch, that time would be correctly shown as: 1900-01-01 00:01:39.999999999
- The sys_time formatter is constrained, which was not implemented. - There is a sys_days formatter which was not implemented. - The local_time formatter uses the sys_time formatter in its implementation so "inherited" the same issues. Fixes: https://github.com/llvm/llvm-project/issues/73849 Fixes: https://github.com/llvm/llvm-project/issues/67983