Hashing differences

[wolfv]

There are slight differences in the contents in get_hash_dependencies to compute the build string:

• [ ] conda includes CONDA_BUILD_SYSROOT
• [ ] conda includes channel_targets
• [ ] conda seems to not include build deps except compilers?
• [ ] if only target_platform in the variant, conda disregards that

[wolfv]

We might have to implement the trim_build_only_deps better. But all this logic is so finnicky ... I am still not sure how to approach this.