Add GCC to the build environment.

Needed for the RP2040 bootloader.

Author: thejpster

.github/workflows/rust.yml

@@ -12,6 +12,8 @@ jobs:
       uses: actions/checkout@v1
       with:
         submodules: true
+    - name: Install GCC ARM
+      run: sudo apt-get update && sudo apt-get install -y gcc-arm-none-eabi
     - name: Add Target
       run: rustup target add thumbv6m-none-eabi
     - name: Build