Build warning C4127 on Windows using MSVC 19.26.288806 in C++20 mode

[mbeckh]

The code

std::string x = fmt::format("{}", std::chrono::system_clock::now().time_since_epoch())

produces warning C4127 ("conditional expression is constant, consider using 'if constexpr' statement instead") for the following lines

fmt\chrono.h: line 75
fmt\chrono.h: line 83
fmt\chrono.h: line 94
fmt\chrono.h: line 96
fmt\chrono.h: line 197
fmt\chrono.h: line 213

Latest verification of warning with master at commit f9f02df.

[vitaut]

https://github.com/fmtlib/fmt/blob/master/include/fmt/chrono.h#L75 and similar should be wrapped in a call to const_check. A PR is welcome.

[vitaut]

Suppressed the warnings in #1825.