machinst x64: add testing to the CI;

.github/workflows/main.yml

@@ -269,6 +269,45 @@ jobs:
       env:
         RUST_BACKTRACE: 1
 
+  # Perform all tests (debug mode) for `wasmtime` with the experimental x64
+  # backend. This runs on the nightly channel of Rust (because of issues with
+  # unifying Cargo features on stable) on Ubuntu.
+  test_x64:
+    name: Test x64 new backend
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+      with:
+        submodules: true
+    - uses: ./.github/actions/install-rust
+      with:
+        toolchain: nightly-2020-07-27
+    - uses: ./.github/actions/define-llvm-env
+
+    # Install wasm32 targets in order to build various tests throughout the
+    # repo
+    - run: rustup target add wasm32-wasi
+    - run: rustup target add wasm32-unknown-unknown
+
+    # Build and test all features except for lightbeam
+    - run: |
+        cargo \
+            -Zfeatures=all -Zpackage-features \
+            test \
+            --features test-programs/test_programs \
+            --features experimental_x64 \
+            --all \
+            --exclude lightbeam \
+            --exclude peepmatic \
+            --exclude peepmatic-automata \
+            --exclude peepmatic-fuzzing \
+            --exclude peepmatic-macro \
+            --exclude peepmatic-runtime \
+            --exclude peepmatic-test
+      env:
+        RUST_BACKTRACE: 1
+
+
   # Verify that cranelift's code generation is deterministic
   meta_determinist_check:
     name: Meta deterministic check