Adds find_package for fmtlib, range-v3, nlohmann_json

[clonker]

Adds find_package for fmtlib, range-v3, nlohmann_json if IGNORE_VENDORED_DEPENDENCIES was set to ON.

Fixes #15872

[aarlt]

hmm.. I just saw this - the question is basically how the stuff is used.. the use-case that I had in mind when I was doing this, was to just being able to easily embed solidity into another project - where the "root" cmake file will find needed packages.. I'm not sure right now why I exactly not just added the find_packages there - but maybe we should at least have a mechanism that will not call find the needed packages automatically - so that the "root" cmake file is still under control

[aarlt]

However, I don't see the reason right now why I didn't just call find_package there. I think it should be totally fine, even without that special flag. I thought there was a good reason not to call it there, but apparently I don't remember that right now.

[aarlt]

Ok, I just remembered the issue, why I decided not to use find_package in this case. The issue was that we had internally for jsoncpp a different target name as normally defined by the official one (see aarlt/cmake_vcpkg_solidity@2679ec0#diff-1e7de1ae2d059d21e1dd75d5812d5a34b0222cef273b7c3a2af62eb747f9d20aR16) so I thought it would be the best, if a "root" cmake file is dealing with the aliases. However, because we don't use that anymore we can just do it as you implemented it.

[aarlt]

The only thing that could make some sense for some users is to allow them to ignore specific versions of the libraries. E.g. by default we use exactly what you have defined, but if e.g. something like IGNORE_SPECIFIC_DEPENDENCY_VERSIONS was set, it will just use any version.

[Spixmaster]

Indeed, having specific versions will break packages like https://aur.archlinux.org/packages/solidity.

[clonker]

Indeed, having specific versions will break packages like https://aur.archlinux.org/packages/solidity.

For this particular package I don't see how this change would lead to breakage. It has IGNORE_VENDORED_DEPENDENCIES set to OFF, therefore the three dependencies are pulled in as submodules. But I agree, the version should probably only be restricted to a major version - if at all.

[Spixmaster]

The reason that -D IGNORE_VENDORED_DEPENDENCIES=OFF is set is due to this bug #15872. Otherwise, the option would be set to ON.

I am the package maintainer.