Add CI workflow to test null-safety feature

- Create test-null-safety.yml workflow that runs on push/PR
- Builds clang with assertions enabled
- Runs strict-nullability.c test suite via llvm-lit
- Fails CI if null-safety tests fail
- Add status badge to README showing test status

Now the README will show a green badge if tests pass, red if failing!

Author: cs01

.github/workflows/test-null-safety.yml

@@ -0,0 +1,50 @@
+name: Test Null-Safety
+
+on:
+  push:
+    branches:
+      - null-safe-c-dev
+  pull_request:
+    branches:
+      - null-safe-c-dev
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y ninja-build cmake build-essential
+
+      - name: Configure build
+        run: |
+          mkdir -p build
+          cd build
+          cmake -G Ninja \
+            -DCMAKE_BUILD_TYPE=Release \
+            -DLLVM_ENABLE_PROJECTS="clang" \
+            -DLLVM_TARGETS_TO_BUILD="X86" \
+            -DLLVM_ENABLE_ASSERTIONS=ON \
+            -DLLVM_INCLUDE_TESTS=ON \
+            ../llvm
+
+      - name: Build Clang and test tools
+        run: |
+          cd build
+          ninja clang FileCheck count not
+
+      - name: Run strict-nullability tests
+        run: |
+          cd build
+          ./bin/llvm-lit -v ../clang/test/Sema/strict-nullability.c
+
+      - name: Test results
+        if: success()
+        run: |
+          echo "✅ All null-safety tests passed!"

README.md

@@ -1,5 +1,7 @@
 # Null-Safe Clang: An experimental C/C++ compiler
 
+[![Test Null-Safety](https://github.com/cs01/llvm-project/actions/workflows/test-null-safety.yml/badge.svg)](https://github.com/cs01/llvm-project/actions/workflows/test-null-safety.yml)
+
 An experimental Clang fork that adds flow-sensitive null safety to C and C++, inspired by modern languages like TypeScript, Kotlin, and Rust.
 
 **Try it online:** [Interactive Playground](https://cs01.github.io/llvm-project/) - See null-safety warnings in real-time in your browser!