Allow building against different fmt versions

[xvitaly]

Allow building against different fmt versions. Very useful for GNU/Linux.

[BillyONeal]

This is broken because you've tried to include a header in its fwd header.

Can you provide a meaningful justification for this? We aren't supporting any configuration that isn't the one that CMakeLists is going to give you.

[xvitaly]

This is broken because you've tried to include a header in its fwd header.

Everything builds as expected. All tests passed.

Can you provide a meaningful justification for this? We aren't supporting any configuration that isn't the one that CMakeLists is going to give you.

Some GNU/Linux distributions (Fedora Linux for example) have vcpkg in their repositories and we need to be able to build vcpkg against different fmt versions (currently we only have fmt 10 in unreleased development branch).

[BillyONeal]

Some GNU/Linux distributions (Fedora Linux for example) have vcpkg in their repositories and we need to be able to build vcpkg against different fmt versions (currently we only have fmt 10 in unreleased development branch).

How do you get the rest of the supporting files vcpkg needs to be reasonable?

[xvitaly]

How do you get the rest of the supporting files vcpkg needs to be reasonable?

All other sources are okay and can be built with fmt 8.0 - 10. The problem is the use of the inline namespace fmt::vX in include/vcpkg/base/fwd/format.h.

Maybe it can be rewritten with using a custom formatter without changing fmt's namespace?

[xvitaly]

https://fmt.dev/latest/api.html#formatting-user-defined-types

[xvitaly]

microsoft/vcpkg#32784