Add CI job for AVX2 builds. (#1723)

Summary: Pull Request resolved: https://github.com/facebookresearch/faiss/pull/1723

Reviewed By: mdouze

Differential Revision: D26814122

Pulled By: beauby

fbshipit-source-id: ef7ea57b497e314960319c695ea46f22de208054

.circleci/config.yml

@@ -28,6 +28,10 @@ jobs:
              fi
 
   build_linux:
+    parameters:
+      opt_level:
+        type: string
+        default: generic
     docker:
       - image: beauby/faiss-circleci:cpu
     environment:
@@ -39,6 +43,7 @@ jobs:
           name: Build faiss library
           command: |
             cmake -B build -DBUILD_TESTING=ON -DFAISS_ENABLE_GPU=OFF \
+                  -DFAISS_OPT_LEVEL=<< parameters.opt_level >> \
                   -DFAISS_ENABLE_C_API=ON \
                   -DCMAKE_BUILD_TYPE=Release -DBLA_VENDOR=Intel10_64_dyn .
             make -C build -j faiss
@@ -252,6 +257,9 @@ workflows:
           name: Format
       - build_linux:
           name: Linux
+      - build_linux:
+          name: Linux (AVX2)
+          opt_level: "avx2"
       - build_linux_gpu:
           name: Linux GPU
           requires: