Split CI jobs

Intended benefits

- More parallelism

- Failures are clearer at a glance

.github/workflows/rust.yml

@@ -14,7 +14,7 @@ env:
   CARGO_TERM_COLOR: always
 
 jobs:
-  clippy_fmt_test:
+  clippy:
     runs-on: ubuntu-latest
 
     strategy:
@@ -26,29 +26,83 @@ jobs:
         uses: fiam/[email protected]
         with:
           release: '9-2019-q4'
-      - name: Install clang
-        run: sudo apt-get update && sudo apt install -y clang
       - name: Install toolchains
         uses: actions-rs/toolchain@v1
         with:
           toolchain: nightly
-          default: true
-          components: rust-src, rustfmt, clippy
+          override: true
+          components: rust-src, clippy
       - uses: actions/checkout@v2
       - name: Cargo clippy
         uses: actions-rs/cargo@v1
         with:
           command: clippy
-          args: -Z build-std=core --target ./${{ matrix.target }}.json -- -D warnings
+          args: --target ./${{ matrix.target }}.json
+  fmt:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Install toolchains
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          override: true
+          components: rust-src, rustfmt
+      - uses: actions/checkout@v2
       - name: Cargo fmt
         uses: actions-rs/cargo@v1
         with:
           command: fmt
           args: --all -- --check
+
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target: ["nanos", "nanox", "nanosplus"]
+
+    steps:
+      - name: arm-none-eabi-gcc
+        uses: fiam/[email protected]
+        with:
+          release: '9-2019-q4'
+      - name: Install clang
+        run: sudo apt-get update && sudo apt install -y clang
+      - name: Install toolchains
+        uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          override: true
+          components: rust-src
+      - uses: actions/checkout@v2
+      - name: Cargo build
+        uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --target ./${{ matrix.target }}.json
+
+  test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        target: ["nanos", "nanox", "nanosplus"]
+
+    steps:
+      - name: arm-none-eabi-gcc
+        uses: fiam/[email protected]
+        with:
+          release: '9-2019-q4'
+      - name: Install clang
+        run: sudo apt-get update && sudo apt install -y clang
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: nightly
+          override: true
+          components: rust-src
       - name: Install dependencies
         run: |
           sudo apt-get update && sudo apt-get install -y qemu-user-static
           pip install speculos --extra-index-url https://test.pypi.org/simple/
+      - uses: actions/checkout@v2
       - name: Unit tests
         uses: actions-rs/cargo@v1
         with: