Run WASM for multiple toolchains

WASM is supported by Rust 1.30. We can therefore run the WASM tests on
any all the toolchains except MSRV (1.29.0). This has benefit of
catching nightly/beta issues before they get to stable.

Done as a separate CI job since it is conceptually different to the
`Tests` job.

Run WASM for nightly, beta, and stable toolchains.

.github/workflows/rust.yml

@@ -36,20 +36,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        include:
+        rust: [stable, beta, nightly, 1.29.0]
-          - rust: stable
-            env:
-              DO_FEATURE_MATRIX: true
-              DO_WASM: true
-          - rust: beta
-            env:
-              DO_FEATURE_MATRIX: true
-          - rust: nightly
-            env:
-              DO_FEATURE_MATRIX: true
-          - rust: 1.29.0
-            env:
-              DO_FEATURE_MATRIX: true
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v2
@@ -63,6 +50,29 @@ jobs:
         if: matrix.rust == '1.29.0'
         run: cargo generate-lockfile --verbose && cargo update -p cc --precise "1.0.41" --verbose
       - name: Running cargo
-        env: ${{ matrix.env }}
+        env:
+          DO_FEATURE_MATRIX: true
         run: ./contrib/test.sh
 
+  WASM:
+    name: WASM
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        rust: [stable, beta, nightly] # No 1.29 because WASM requires Rust 1.30
+    steps:
+      - name: Checkout Crate
+        uses: actions/checkout@v2
+      - name: Install clang
+        run: sudo apt-get install -y clang-9
+      - name: Checkout Toolchain
+        uses: actions-rs/toolchain@v1
+        with:
+          profile: minimal
+          toolchain: ${{ matrix.rust }}
+          override: true
+          components: rust-src
+      - name: Running WASM tests
+        env:
+          DO_WASM: true
+        run: ./contrib/test.sh