crystal: optimize the build command even further

[renich]

It's suggested that you build with: --release --no-debug in order to optimize for performance.

Also, the documentation states the following about --mcpu=:

               --mcpu CPU
                         Specify a specific CPU to generate code for. This will pass a -mcpu flag to LLVM, and is only intended to be used for cross-compilation. For
                         a list of available CPUs, invoke "llvm-as < /dev/null | llc -march=xyz -mcpu=help".  Passing --mcpu native will pass the host CPU name to
                         tune performance for the host.

If we are to use it, then, at the very least, use --mcpu=native.

[hanabi1224]

Thanks, but it's intended to use --mcpu=broadwell for all launguages