Update softmixer.rs to use AtomicU64 from atomic_shim, so that librespot works with MIPS and MIPSEL

[humaita-github]

MIPS and MIPSEL [and PowerPC (?)] don't support AtomicU64, since they are 32 bit. However, there is a crate that provides shims for these platforms. When it detects it is running on unsupported platforms, it fallbacks to the shim implementation, using crossbeam Mutex. For supported platforms, there should be no change.

See initial discussion in #1460

[photovoltex]

Would you be so kind to fix the compilation issues?

[humaita-github]

Hi, sorry for the back and forth -- I am new to rust. All should be fixed now.

[photovoltex]

No probs, everyone starts at some point :). Just try to check next time that at least it compiles before submitting a PR^^;

[humaita-github]

Hi, it turns out that atomic_shim works for MIPS and MIPSEL, but not for ARM. However, portable-atomic seems to work well for all targets. I will create a new pull request

[photovoltex]

But shouldn't that have been caught by the CI? And what do you mean exactly by it does "not work" for ARM?

[humaita-github]

Hi, yes it should have been caught, but it didn't. I am compiling for ~ 15 different ARM flavours, and unfortunately I didn't take note on which one was failing, it might have been ARMv5 or ARMv7. The error is the same as MIPS show without atomic_shim or similar:

PS: The problems with ARM, MIPS and PowerPC are mentioned here: https://doc.rust-lang.org/core/sync/atomic/#portability