as: unrecognized option '-mcpu=cortex-a5' ninja: build stopped: subcommand failed.

This error message suggests that the compiler is unable to recognize the option "-mcpu=cortex-a5". This option is used to specify the target CPU architecture for the compilation process.

One possible reason for this error could be that the compiler version being used does not support the "-mcpu=cortex-a5" option. In that case, you may need to upgrade the compiler to a version that supports this option.

Another possible reason could be a typo in the command or a missing dependency. Double-check the command and make sure that all required dependencies are installed and available.

If you are still unable to resolve the issue, you may need to seek further assistance from the compiler or platform documentation, or from a support forum specific to your platform or toolchain.