I started this diff trying to remove a little dead code from the C
backend, but ended up finding a bunch of dead code sprinkled all over
the place:
* `packed` handling in the C backend which was made dead by `Legalize`
* Representation of pointers to runtime-known vector indices
* Handling for the `vector_store_elem` AIR instruction (now removed)
* Old tuple handling from when they used the InternPool repr of structs
* Straightforward unused functions
* TODOs in the LLVM backend for features which Zig just does not support
they seem to be always `null` even when accessed through extern key so we have no way to tell whether they have natural alignment or not to decorate. And the reason we don't always decorate them is because some environments might be too dumb and crash for this.
ashpil