Fix warnings for compilers with EDG frontend

[phprus]

1) warning: a class type that is not trivially copyable passed through ellipsis (EDG frontend)

lcc: "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/core.h", line 1670: warning #1290:
          a class type that is not trivially copyable passed through ellipsis
      return vis(sv(arg.value_.string.data, arg.value_.string.size));
                 ^
          detected during:
            instantiation of
                      "auto fmt::v9::visit_format_arg(Visitor &&, const fmt::v9::basic_format_arg<Context> &)->decltype((<expression>)) [with Visitor=fmt::v9::detail::loc_writer<char> &, Context=fmt::v9::format_context]"
                      at line 1022 of
                      "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/format.h"
            instantiation of
                      "auto fmt::v9::loc_value::visit(Visitor &&)->decltype((<expression>)) [with Visitor=fmt::v9::detail::loc_writer<char>]"
                      at line 146 of
                      "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/format-inl.h"

lcc: "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/core.h", line 1674: warning #1290:
          a class type that is not trivially copyable passed through ellipsis
      return vis(typename basic_format_arg<Context>::handle(arg.value_.custom));
                 ^
          detected during:
            instantiation of
                      "auto fmt::v9::visit_format_arg(Visitor &&, const fmt::v9::basic_format_arg<Context> &)->decltype((<expression>)) [with Visitor=fmt::v9::detail::loc_writer<char> &, Context=fmt::v9::format_context]"
                      at line 1022 of
                      "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/format.h"
            instantiation of
                      "auto fmt::v9::loc_value::visit(Visitor &&)->decltype((<expression>)) [with Visitor=fmt::v9::detail::loc_writer<char>]"
                      at line 146 of
                      "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/format-inl.h"

lcc: "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/core.h", line 1676: warning #1290:
          a class type that is not trivially copyable passed through ellipsis
    return vis(monostate());
               ^
          detected during:
            instantiation of
                      "auto fmt::v9::visit_format_arg(Visitor &&, const fmt::v9::basic_format_arg<Context> &)->decltype((<expression>)) [with Visitor=fmt::v9::detail::loc_writer<char> &, Context=fmt::v9::format_context]"
                      at line 1022 of
                      "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/format.h"
            instantiation of
                      "auto fmt::v9::loc_value::visit(Visitor &&)->decltype((<expression>)) [with Visitor=fmt::v9::detail::loc_writer<char>]"
                      at line 146 of
                      "/export/home/phprus/fmt/fmt-hexfloat-1/include/fmt/format-inl.h"

Passing a non-trivially copyable class via ... is not allowed:

Only arithmetic, enumeration, pointer, pointer to member, and class type arguments (after conversion) are allowed. However, non-POD class types (until C++11)class types with an eligible non-trivial copy constructor, an eligible non-trivial move constructor, or a non-trivial destructor, together with scoped enumerations (since C++11), are conditionally-supported in potentially-evaluated calls with implementation-defined semantics (these types are always supported in unevaluated calls).

See: https://en.cppreference.com/w/cpp/language/variadic_arguments

2) warning: the implicit by-copy capture of "this" is deprecated (EDG frontend)

lcc: "/export/home/phprus/fmt/fmt-hexfloat-1/test/gtest/gmock-gtest-all.cc", line 13783: warning #2908:
          the implicit by-copy capture of "this" is deprecated
                 ? this->UntypedPerformDefaultAction(untyped_args, ss.str())
                   ^

I think it's a bug in the compiler or EDG frontend.

[vitaut]

Thanks!