Fix LGTM C++ failure: always use Python3 for lgtm C/C++ (onnx#3981)

* use Python 3

Signed-off-by: Chun-Wei Chen <jacky82226@gmail.com>

Author: jcwchen

.lgtm.yml

@@ -0,0 +1,20 @@
+# By default, C/C++ extraction from LGTM.com uses Python 2
+# Add this file to make it use Python 3
+# Build protobuf from source with -fPIC is required here to prevent protobuf symbol error
+extraction:
+  cpp:
+    before_index:
+      # Always use Python 3
+      - cp `which python3` $LGTM_WORKSPACE/python
+      - PATH=$LGTM_WORKSPACE:$PATH
+      # Build protobuf from source with -fPIC
+      - git clone https://github.com/protocolbuffers/protobuf.git
+      - cd protobuf
+      - git checkout v3.16.0
+      - git submodule update --init --recursive
+      - mkdir build_source && cd build_source
+      # Cannot use sudo so install locally at $HOME/protobuffers
+      - cmake ../cmake -Dprotobuf_BUILD_SHARED_LIBS=OFF -DCMAKE_INSTALL_PREFIX=$HOME/protobuffers -DCMAKE_INSTALL_SYSCONFDIR=/etc -DCMAKE_POSITION_INDEPENDENT_CODE=ON -Dprotobuf_BUILD_TESTS=OFF -DCMAKE_BUILD_TYPE=Release
+      - make -j$(nproc)
+      - make install
+      - PATH=$HOME/protobuffers/bin:$PATH

setup.cfg

@@ -9,6 +9,8 @@ testpaths = onnx/test onnx/examples
 
 [metadata]
 license_files = LICENSE
+classifiers =
+    Programming Language :: Python :: 3
 
 [flake8]
 select = B,C,E,F,P,T4,W,B9