warning C4127: conditional expression is constant

[apache-hb]

building the latest commit (95da484) with /W4 with msvc 19.27.29111 yields the following diagnostic

fmt\core.h(399): warning C4127: conditional expression is constant
fmt\core.h(399): note: consider using 'if constexpr' statement instead
fmt\core.h(398): note: while compiling class template member function 'fmt::v7::basic_string_view<wchar_t>::basic_string_view(const Char *)'
        with
        [
            Char=wchar_t
        ]
fmt\src\os.cc(126): note: see reference to function template instantiation 'fmt::v7::basic_string_view<wchar_t>::basic_string_view(const Char *)' being compiled
        with
        [
            Char=wchar_t
        ]
fmt\format.h(1222): note: see reference to class template instantiation 'fmt::v7::basic_string_view<wchar_t>' being compiled