repo: add CI no_std check

.github/workflows/rust.yml

@@ -11,7 +11,6 @@ env:
 
 jobs:
   build:
-
     runs-on: ubuntu-latest
     strategy:
         matrix:
@@ -26,6 +25,21 @@ jobs:
     - name: Run tests
       run: cargo test --verbose
 
+  build_no_std:
+      runs-on: ubuntu-latest
+      strategy:
+          matrix:
+              rust:
+                  - stable
+                  - nightly
+                  - 1.52.1 # MSVR
+      steps:
+          -   uses: actions/checkout@v2
+          -   name: "Rustup: install some no_std target"
+              run: rustup target add thumbv7em-none-eabihf
+          -   name: Build (no_std)
+              run: cargo build --target thumbv7em-none-eabihf
+
 
   # As discussed, these tasks are optional for PRs.
   style_checks: