CI: LLVM toolchain build-only validation

This configures CI to use LLVM toolchain for build validation only:
- LLVM: Build kernel and library (compilation verification)
- LLVM: Skip crash tests and functional tests
- GNU: Full test suite (build + crash tests + functional tests)

Author: jserv

.github/workflows/ci.yml

@@ -51,6 +51,7 @@ jobs:
       - name: Run All Apps
         id: test
         continue-on-error: true
+        if: matrix.toolchain == 'gnu'
         run: |
           output=$(.ci/run-app-tests.sh 2>&1) || true
           echo "TEST_OUTPUT<<EOF" >> $GITHUB_OUTPUT
@@ -62,6 +63,7 @@ jobs:
       - name: Run Functional Tests
         id: functional_test
         continue-on-error: true
+        if: matrix.toolchain == 'gnu'
         run: |
           output=$(.ci/run-functional-tests.sh 2>&1) || true
           echo "FUNCTIONAL_TEST_OUTPUT<<EOF" >> $GITHUB_OUTPUT
@@ -73,7 +75,20 @@ jobs:
       - name: Collect Test Data
         if: always()
         run: |
-          .ci/ci-tools.sh collect-data "${{ matrix.toolchain }}" "${{ steps.test.outputs.TEST_OUTPUT }}" "${{ steps.functional_test.outputs.FUNCTIONAL_TEST_OUTPUT }}"
+          if [ "${{ matrix.toolchain }}" = "llvm" ]; then
+            # LLVM: Build-only validation, skip tests
+            mkdir -p test-results
+            echo "${{ matrix.toolchain }}" > test-results/toolchain
+            echo "0" > test-results/crash_exit_code
+            echo "0" > test-results/functional_exit_code
+            touch test-results/apps_data
+            touch test-results/functional_data
+            touch test-results/functional_criteria_data
+            echo "LLVM toolchain: Build validation only (tests skipped)"
+          else
+            # GNU: Full test suite
+            .ci/ci-tools.sh collect-data "${{ matrix.toolchain }}" "${{ steps.test.outputs.TEST_OUTPUT }}" "${{ steps.functional_test.outputs.FUNCTIONAL_TEST_OUTPUT }}"
+          fi
 
       - name: Upload Test Results
         if: always()