Currently some `Allocation`s are interned, some are not, and it's very
hard to tell at a use point which is which.
This commit introduces `ConstAllocation` for the known-interned ones,
which makes the division much clearer. `ConstAllocation::inner()` is
used to get the underlying `Allocation`.
In some places it's natural to use an `Allocation`, in some it's natural
to use a `ConstAllocation`, and in some places there's no clear choice.
I've tried to make things look as nice as possible, while generally
favouring `ConstAllocation`, which is the type that embodies more
information. This does require quite a few calls to `inner()`.
The commit also tweaks how `PartialOrd` works for `Interned`. The
previous code was too clever by half, building on `T: Ord` to make the
code shorter. That caused problems with deriving `PartialOrd` and `Ord`
for `ConstAllocation`, so I changed it to build on `T: PartialOrd`,
which is slightly more verbose but much more standard and avoided the
problems.
* Make define_global() return a RValue directly
* Return LValue in functions declaring a global variable
* Remove useless cast
* Fix bytes_in_context to use an array rvalue
* Remove global_names which is unused
* Make const_struct create a constant struct
* Correctly initialize global in static_addr_of_mut
* Fix global variable initialization
* Remove workaround for ARGV
* Implement `black_box` as intrinsic
Responsibility of implementing the black box is now lies on backend
* Remove some TODOs
* Update to nightly-2021-09-17
* CI: don't fail on warnings
