Doesn't compile with newest nightly

[tyllmoritz]

I tried compiling this with the newest nightly and ran into some Issues:

With toolchain nightly-2022-04-26 and newer I had the following error:

• rust-lld: error: […].rcgu.o: cannot link object files with different floating-point ABI

With toolchain nightly-2022-06-22 and newer I had the following error:

• libstd: -Z build-std is now broken …

With toolchain nightly-2022-08-13 and newer I had the following error:

• rust-lld: error: […]expected filename pattern >>> (*(.trap));
• riscv-rt doesn't compile with the latest nightly toolchain.

As soon as a current nightly is working, we can try to enable the RISC-V Bitmanip extensions:
rust-lang/rust@be8fd0e
perhaps it's just as easy as adding the following line to the target-spec-json.

"features": "+m,+a,+c,+f,+zba,+zbb",

rustc +nightly -Z unstable-options --print target-spec-json --target riscv32imac-unknown-none-elf | jq -S '."is-builtin"=false | ."features"=("+m,+a,+c,+f,+zba,+zbb") | . + {"llvm-abiname":"ilp32f","executables":true}' | tee riscv32imafbc-unknown-none-elf.json