ci: Install the cross-compiler toolchains

Use `apt-get` to install `mingw-w64` and `llvm`.

Author: ravenexp

.github/workflows/rust.yml

@@ -11,11 +11,12 @@ env:
 
 jobs:
   build:
-
+    name: Build and test
     runs-on: ubuntu-latest
-
     steps:
     - uses: actions/checkout@v3
+    - name: Install the MinGW and LLVM toolchains
+      run: sudo apt-get install -y mingw-w64 llvm
     - name: Build
       run: cargo build --verbose
     - name: Run tests