Use new CMake-based OSS c++ gtest workflow

For OSS, we should focus on CMake build. Now we can build c++ tests, we
should run them with cmake built tests.

Author: kirklandsign

.github/workflows/_unittest.yml

@@ -15,10 +15,6 @@ on:
 jobs:
   linux:
     uses: pytorch/test-infra/.github/workflows/linux_job.yml@main
-    strategy:
-      matrix:
-        include:
-          - build-tool: buck2
     with:
       runner: linux.2xlarge
       docker-image: ${{ inputs.docker-image }}
@@ -32,23 +28,19 @@ jobs:
         CONDA_ENV=$(conda env list --json | jq -r ".envs | .[-1]")
         conda activate "${CONDA_ENV}"
 
-        BUILD_TOOL=${{ matrix.build-tool }}
-
         # Setup MacOS dependencies as there is no Docker support on MacOS atm
         PYTHON_EXECUTABLE=python \
         EXECUTORCH_BUILD_PYBIND=ON \
         EXECUTORCH_BUILD_XNNPACK=ON \
-        .ci/scripts/setup-linux.sh "${BUILD_TOOL}"
+        .ci/scripts/setup-linux.sh cmake
 
         # Run pytest with coverage
         pytest -n auto --cov=./ --cov-report=xml
+        # Run gtest
+        sh test/run_oss_cpp_tests.sh
 
   macos:
     uses: pytorch/test-infra/.github/workflows/macos_job.yml@main
-    strategy:
-      matrix:
-        include:
-          - build-tool: buck2
     with:
       runner: macos-m1-stable
       python-version: '3.11'
@@ -57,18 +49,17 @@ jobs:
       script: |
         set -eux
 
-        BUILD_TOOL=${{ matrix.build-tool }}
-
         bash .ci/scripts/setup-conda.sh
 
         # Setup MacOS dependencies as there is no Docker support on MacOS atm
         PYTHON_EXECUTABLE=python \
         EXECUTORCH_BUILD_PYBIND=ON \
         CMAKE_ARGS="-DEXECUTORCH_BUILD_COREML=ON -DEXECUTORCH_BUILD_MPS=ON -DEXECUTORCH_BUILD_XNNPACK=ON" \
         ${CONDA_RUN} --no-capture-output \
-        .ci/scripts/setup-macos.sh "${BUILD_TOOL}"
+        # TODO: Migrate to cmake
+        .ci/scripts/setup-macos.sh buck2
 
         # Run pytest with coverage
         ${CONDA_RUN} pytest -n auto --cov=./ --cov-report=xml
-        # Run gtest
+        # Run gtest. TODO: Migrate to cmake
         ${CONDA_RUN} buck2 test runtime/core/... runtime/platform/...