Make UnknownPlatform a wrapper of Platform

[mkitti]

One source of invalidations results from defining tags(::Pkg.BinaryPlatforms.UnknownPlatform).

This pull request homogenizes the issue so that UnknownPlatform is now a wrapper around Platform and is now part of the PlatformUnion.

 inserting tags(::Pkg.BinaryPlatforms.UnknownPlatform) @ Pkg.BinaryPlatforms ~/src/julia/usr/share/julia/stdlib/v1.11/Pkg/src/BinaryPlatforms_compat.jl:17 invalidated:
   mt_backedges:  1: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.triplet(::Base.BinaryPlatforms.AbstractPlatform) (0 children)
                  2: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.os_version(::Base.BinaryPlatforms.AbstractPlatform) (1 children)
                  3: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.libgfortran_version(::Base.BinaryPlatforms.AbstractPlatform) (1 children)
                  4: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.cxxstring_abi(::Base.BinaryPlatforms.AbstractPlatform) (1 children)
                  5: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.libstdcxx_version(::Base.BinaryPlatforms.AbstractPlatform) (1 children)
                  6: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.arch(::Base.BinaryPlatforms.AbstractPlatform) (2 children)
                  7: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.os(::Base.BinaryPlatforms.AbstractPlatform) (2 children)
                  8: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.libc(::Base.BinaryPlatforms.AbstractPlatform) (2 children)
                  9: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.call_abi(::Base.BinaryPlatforms.AbstractPlatform) (2 children)
                 10: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.platforms_match(::Base.BinaryPlatforms.AbstractPlatform, ::Base.BinaryPlatforms.Platform) (17 children)
                 11: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for (::Base.BinaryPlatforms.var"#match_loss#50")(::Base.BinaryPlatforms.AbstractPlatform, ::Base.BinaryPlatforms.Platform) (40 children)

[mkitti]

This just shifts the problem slightly, so that now the tags(p::PlatformUnion) is the thing that invalidates tags(::AbstractPlatform). The idea though is that we're working so that we do convert(Platform, p::PlatformUnion) = p.p.

 inserting tags(p::Union{Pkg.BinaryPlatforms.FreeBSD, Pkg.BinaryPlatforms.Linux, Pkg.BinaryPlatforms.MacOS, Pkg.BinaryPlatforms.UnknownPlatform, Pkg.BinaryPlatforms.Windows}) @ Pkg.BinaryPlatforms ~/src/Pkg.jl/src/BinaryPlatforms_compat.jl:86 invalidated:
   mt_backedges:  1: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.triplet(::Base.BinaryPlatforms.AbstractPlatform) (0 children)
                  2: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.os_version(::Base.BinaryPlatforms.AbstractPlatform) (1 children)
                  3: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.libgfortran_version(::Base.BinaryPlatforms.AbstractPlatform) (1 children)
                  4: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.cxxstring_abi(::Base.BinaryPlatforms.AbstractPlatform) (1 children)
                  5: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.libstdcxx_version(::Base.BinaryPlatforms.AbstractPlatform) (1 children)
                  6: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.arch(::Base.BinaryPlatforms.AbstractPlatform) (2 children)
                  7: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.os(::Base.BinaryPlatforms.AbstractPlatform) (2 children)
                  8: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.libc(::Base.BinaryPlatforms.AbstractPlatform) (2 children)
                  9: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.call_abi(::Base.BinaryPlatforms.AbstractPlatform) (2 children)
                 10: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for Base.BinaryPlatforms.platforms_match(::Base.BinaryPlatforms.AbstractPlatform, ::Base.BinaryPlatforms.Platform) (13 children)
                 11: signature Tuple{typeof(Base.BinaryPlatforms.tags), Base.BinaryPlatforms.AbstractPlatform} triggered MethodInstance for (::Base.BinaryPlatforms.var"#match_loss#50")(::Base.BinaryPlatforms.AbstractPlatform, ::Base.BinaryPlatforms.Platform) (30 children)

[mkitti]

The real solution to the invalidation issue is JuliaLang/julia#54073 . This, however, is an important step to help get there.