Fix riscv32 atomics and fix tests on 32-bit platforms

[xobs]

This fixes tests on 32-bit platforms. Previously, the Encode would encode a usize and decode a u64. This works fine on 64-bit platforms, but on 32-bit platforms this results in a mismatch.

Force usize to be encoded as a u64 even on 32-bit platforms.

Additionally, the 32-bit riscv target does not implement AtomicU64 or AtomicI64, so remove those impelementations on that platform.

[VictorKoenders]

I wonder if we could make this bigger and add target_has_atomic to all atomic impls, and deprecate the atomic feature

[xobs]

Thanks for the suggestions. I've annotated all Atomic implementations.

I assume that Bool is the same as 8, and usize is the same as ptr.

I'm not sure what the best way is to deprecate the feature, so I removed it wholesale.

[codecov]

Codecov Report

Merging #533 (b7f1a1d) into trunk (36ab23c) will decrease coverage by 1.36%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##            trunk     #533      +/-   ##
==========================================
- Coverage   70.82%   69.45%   -1.37%     
==========================================
  Files          47       46       -1     
  Lines        3215     3179      -36     
==========================================
- Hits         2277     2208      -69     
- Misses        938      971      +33     

Impacted Files	Coverage Δ
src/atomic.rs	0.00% <ø> (ø)
src/lib.rs	68.75% <ø> (ø)
tests/alloc.rs	92.42% <ø> (ø)
tests/atomic.rs

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[VictorKoenders]

Can you pull in the new cross-platform build pipeline, and see if bincode now compiles for your target arch?

[xobs]

It does build for my platform still, so it looks good to me!

[10:10:39 am] E:/Code/bincode> cargo build --lib --target riscv32imac-unknown-xous-elf
   Compiling virtue v0.0.7
   Compiling bincode_derive v2.0.0-rc.1 (E:\Code\bincode\derive)
   Compiling bincode v2.0.0-rc.1 (E:\Code\bincode)
    Finished dev [unoptimized + debuginfo] target(s) in 2.39s
[10:10:43 am] E:/Code/bincode>

[VictorKoenders]

If you run cargo fmt and cargo clippy I think this is good to merge

[xobs]

Alright, I just ran cargo fmt to fix that up.

[VictorKoenders]

Thanks!