[ci] Use riscv32imac-unknown-none-elf toolchain for no_std check

Author: clabby

.github/scripts/check_no_std.sh

@@ -8,11 +8,16 @@ no_std_packages=(
   commonware-storage
 )
 
-target="thumbv7em-none-eabihf"
+target="riscv32imac-unknown-none-elf"
+image="ghcr.io/commonwarexyz/monorepo/rust-riscv32imac-cross@sha256:652f5ff21c943935bc1caf7cf0c65b38127381c66b423f70f86dc7785d93ce85"
 base_rustflags="${RUSTFLAGS:-}"
 
 for package in "${no_std_packages[@]}"; do
-  build_cmd=(cargo build -p "$package" --no-default-features --target "$target" --release)
+  build_cmd=(docker run \
+    --rm \
+    -v `pwd`:/workdir \
+    -w="/workdir" \
+    "$image" cargo +nightly build -p "$package" -Zbuild-std=core,alloc --no-default-features --target "$target" --release)
   pretty_cmd="${build_cmd[*]}"
   if [ -n "$CI" ]; then
     echo "::group::${pretty_cmd}"

.github/workflows/fast.yml

@@ -176,12 +176,6 @@ jobs:
       uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4
     - name: Run setup
       uses: ./.github/actions/setup
-    - name: Add minimal no_std target
-      run: rustup target add thumbv7em-none-eabihf
-    - name: Install ARM bare-metal toolchain (required to compile C from x86 worker)
-      run: |
-        sudo apt-get update
-        sudo apt-get install -y gcc-arm-none-eabi
     - name: Check no_std compatibility
       run: ./.github/scripts/check_no_std.sh