* format-inl.h(444,1): warning C4804: '>>': unsafe use of type 'bool' in operation
format.h(2808,1): warning C4127: conditional expression is constant
* More fixes for VS2019 pedantic warnings
* Fix "conditional expression is constant" VS2019 warning in more specific way
* Use const_check to silence constexpr warning
* Avoid weak vtables by providing a private virtual member function
* Add warning Wweak-vtables to clang when FMT_PEDANTIC is on
* Add defaulted copy and move operations to format_error and system_error
Compiler generated copy operations are deprecated and move operations
are not generated altogether.
* Add warning Wdeprecated to clang when FMT_PEDANTIC is on
string_view_metadata was introduced to make compiled format relocatable.
However, format string compilation is an optimization and therefore
adding overhead and extra complexity for relocation is undesirable.
In most cases the string will be either static or outlive compilation
and formatting and if it doesn't, it's possible to make compiled
representation relocatale by other means.
gcc-9 gives the following shadow warning:
```
In file included from /Users/libraries/ioss/src/fmt/ostream.h:12,
from /Users/libraries/ioss/src/Ioss_DatabaseIO.C:59:
/Users/libraries/ioss/src/fmt/format.h: In function 'void fmt::v6::internal::parse_format_string(fmt::v6::basic_string_view<Char>, Handler&&)':
/Users/libraries/ioss/src/fmt/format.h:2442:10: warning: declaration of 'struct fmt::v6::internal::parse_format_string(fmt::v6::basic_string_view<Char>, Handler&&)::writer' shadows a global declaration [-Wshadow]
2442 | struct writer {
| ^~~~~~
/Users/libraries/ioss/src/fmt/format.h:1703:7: note: shadowed declaration is here
1703 | using writer = basic_writer<buffer_range<char>>;
| ^~~~~~
```
Since the `writer` struct is only used internally in the `parse_format_string` function, its name can be changed somewhat aribtrarily to avoid conflicts with names in an outer scope.
Note that this warning is also present in the 6.0.0 release.
