cmake_params[1]=-DCMAKE_CXX_FLAGS=-O2 -DNDEBUG
cmake_params[2]=-DCMAKE_CXX_FLAGS=-march=native -O2 -DNDEBUG
# ....

#compile with:

for i in {1..n}
do
    # .. prepare ..
    mkdir build
    cd build
    cmake "${cmake_params[$i]}" ..
    make
done

The CMAKE_CXX_COMPILER:

    clang++ -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_FLAGS=-march=native -O3 -DNDEBUG -DCMAKE_INTERPROCEDURAL_OPTIMIZATION=true -DCMAKE_POLICY_DEFAULT_CMP0069=NEW

   is not a full path and was not found in the PATH.