CI/CD: Downgrade LLVM to 18

.github/workflows/build.yml

@@ -36,7 +36,7 @@ jobs:
 
       - name: Remove unwanted tools
         # Originally from here: https://github.com/AdityaGarg8/remove-unwanted-software/blob/master/action.yml
-        # Modified to keep llvm.
+        # Modified to keep tools nessecary for llvm.
         run: |
           sudo apt-get remove -y '^aspnetcore-.*' > /dev/null
           sudo apt-get remove -y '^dotnet-.*' > /dev/null
@@ -71,6 +71,14 @@ jobs:
           version: latest
           platform: ${{ matrix.arch == 'x86_64' && 'x64' || 'any' }}
 
+      - name: Set up LLVM
+        run: |
+          wget https://apt.llvm.org/llvm.sh
+          chmod +x llvm.sh
+          sudo ./llvm.sh 18
+          sudo apt-get install -y lld-18
+          sudo update-alternatives --install /usr/bin/ld.lld ld.lld /usr/bin/ld.lld-18 100
+
       - name: Check disk space
         run: df -h