Better Error Messages for Uninstalled Tools

[AldaronLau]

For instance if QEMU or objcopy aren't installed.

[CATboardBETA]

This could be pretty easily solved with a simple makefile, if that works for you

[AldaronLau]

I don't really like makefiles. As simple solution would be to just replace the message at https://github.com/ardaku/quantii/blob/stable/xtask/src/main.rs#L106 with "failed to execute aarch64-linux-gnu-objcopy".