Compile benchmarks in CI (#339)

While we don't run benchmarks now, it is still worth to compile the
benchmarks in CI.

.github/workflows/cmake.yml

@@ -30,6 +30,7 @@ jobs:
            sudo mkdir build && cd build
            sudo cmake .. && sudo make
            sudo apt install libgmock-dev -y
+           sudo apt install libbenchmark-dev -y
 
     - name: Configure CMake
       # Configure CMake in a 'build' subdirectory. `CMAKE_BUILD_TYPE` is only required if you are using a single-configuration generator such as make.