[ASPIS] Modified building pipeline, now boardcore library is successfully built

After the optimization passes, the bitcode generated is compiled for the appropriate target and with the c++ compilation flags with clang++.
The compiled object file is then archived in a static library with llvm-ar.
Finally, to create the library in cmake we create an imported library, link it with the miosix interface library and add all the options of boardcore libraries.
Finally is created the alias library Skyward::Boardcore::${BOARD_NAME}