Update rust resolving TARGET=HOST build issues

[heitbaum]

PR that fixes the rust TARGET=HOST build issues

• librespot: fix build where TARGET=HOST with rust 1.54
• system-tools: update to (124)
• bottom: fix build where TARGET=HOST with rust 1.54
• rust: use nightly until 1.54 is released

this was tested with nightly-x86_64-unknown-linux-gnu installed - rustc 1.55.0-nightly (ce1d5611a 2021-06-18)

no planned to be pulled into master until 1.54 is released - 29th July 2021

• Update cargo rust-lang/rust#85926 (cargo update)
• Configure hosts separately from targets when --target is specified. rust-lang/cargo#9322 (patch to cargo)
• Tracking Issue for target-applies-to-host rust-lang/cargo#9453 (Tracking issue)
• https://github.com/rust-lang/rust/milestone/82?closed=1 (1.54 milestone)
• https://doc.rust-lang.org/nightly/cargo/reference/unstable.html?highlight=feature#target-applies-to-host
• Stabilize target-applies-to-host feature. rust-lang/cargo#9753 (Stabilize)

[jameshilliard]

FYI you can use this now in 1.54.0 stable, you just have to set this undocumented env variable to enable nightly features in the stable channel: __CARGO_TEST_CHANNEL_OVERRIDE_DO_NOT_USE_THIS="nightly", something like this.

[heitbaum]

With @jameshilliard ‘s help and __CARGO_TEST_CHANNEL_OVERRIDE_DO_NOT_USE_THIS="nightly" this can now be merged using the stable release of rust - 1.54.0

There should be no issues with updating rust to future versions - but will need to keep a watch on rust-lang/cargo#9753 - at which time the target-applies-to-host option will need to be incorporated without the -Z nightly.

It has been tested building librespot and bottom on

PROJECT=Generic ARCH=x86_64 TARGET_CPU=tigerlake IMAGE_SUFFIX=tigerlake
PROJECT=Rockchip ARCH=aarch64 DEVICE=RK3399 UBOOT_SYSTEM=rock-pi-n10
PROJECT=Rockchip ARCH=arm DEVICE=RK3568 UBOOT_SYSTEM=roc-pc

[CvH]

maybe it works :)

[jameshilliard]

I found a cleaner way to do this in #6104.