build: Enable C unit tests for workflow

.github/workflows/c_tests.yml

@@ -0,0 +1,27 @@
+on: [push, pull_request,repository_dispatch]
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  unitTests:
+    name: C unit tests
+    runs-on: macos-latest
+    env:
+      GEN: ninja
+
+    steps:
+    - name: Install Ninja
+      run: brew install ninja
+
+    - uses: actions/checkout@v2
+      with:
+        fetch-depth: 0
+        submodules: true
+
+    - name: Build Substrait with C unit test
+      run: make release_c_unit_test
+
+    - name: Run C unit tests
+      run: ./build/release/extension/substrait/test/c/test_substrait_exe

Makefile

@@ -29,6 +29,9 @@ release_js: release
 debug_r: debug
 release_r: release
 
+release_c_unit_test:
+	EXT_RELEASE_FLAGS=-DSUBSTRAIT_EXTENSION_TEST_EXE=ON $(MAKE) release
+
 %_python: export BUILD_PYTHON=1
 %_python: export BUILD_FTS=1
 %_python: export BUILD_VISUALIZER=1