Change cmake to build googletest from source (#3319)

Summary:
In the #3278, we to find_package to link to GTest. However, it needs to have googletest to build independently. Not everyone builds their googletest locally first. In this diff, we still try to build googletest from source and combine find_package together.

Pull Request resolved: #3319

Test Plan:
STEP 1: Install deps
```
conda install -y -q python=3.11 cmake make swig=4.0.2 mkl=2023 mkl-devel=2023 numpy scipy pytest gxx_linux-64 sysroot_linux-64
```

STEP2: Compile

```
cmake -B build \
      -DBUILD_TESTING=ON \
      -DBUILD_SHARED_LIBS=ON \
      -DFAISS_ENABLE_GPU=OFF \
      -DFAISS_ENABLE_RAFT=OFF \
      -DFAISS_OPT_LEVEL=avx2 \
      -DFAISS_ENABLE_C_API=ON \
      -DPYTHON_EXECUTABLE=$(which python) \
      -DCMAKE_BUILD_TYPE=Release \
      -DBLA_VENDOR=Intel10_64_dyn \
      -DCMAKE_CUDA_FLAGS="-gencode arch=compute_75,code=sm_75" \
      .
```

Reviewed By: algoriddle

Differential Revision: D55358059

Pulled By: junjieqi

fbshipit-source-id: 95ad4a745238b88b438728de64173f99d3d50dbe

tests/CMakeLists.txt

@@ -59,6 +59,34 @@ if(FAISS_OPT_LEVEL STREQUAL "avx512")
   target_link_libraries(faiss_test PRIVATE faiss_avx512)
 endif()
 
+include(FetchContent)
+FetchContent_Declare(
+  googletest
+  GIT_REPOSITORY https://github.com/google/googletest.git
+  GIT_TAG 58d77fa8070e8cec2dc1ed015d66b454c8d78850 # release-1.12.1
+  OVERRIDE_FIND_PACKAGE)
+set(BUILD_GMOCK CACHE BOOL OFF)
+set(INSTALL_GTEST CACHE BOOL OFF)
+FetchContent_MakeAvailable(googletest)
+
+if(NOT EXISTS ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/gtest-config.cmake
+   AND NOT EXISTS ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/GTestConfig.cmake)
+  file(
+    WRITE ${CMAKE_FIND_PACKAGE_REDIRECTS_DIR}/gtest-config.cmake
+    [=[
+include(CMakeFindDependencyMacro)
+find_dependency(googletest)
+if(NOT TARGET GTest::GTest)
+  add_library(GTest::GTest INTERFACE IMPORTED)
+  target_link_libraries(GTest::GTest INTERFACE GTest::gtest)
+endif()
+if(NOT TARGET GTest::Main)
+  add_library(GTest::Main INTERFACE IMPORTED)
+  target_link_libraries(GTest::Main INTERFACE GTest::gtest_main)
+endif()
+]=])
+endif()
+
 find_package(OpenMP REQUIRED)
 find_package(GTest CONFIG REQUIRED)