Build system rewrite

[tact1m4n3]

Build system rewrite

If anyone has any other ideas of things to add to the new build system (even stuff that was there before and I missed it), please leave a comment in this PR and I will add it to the list.

Tasks to complete

• [x] Initial version of the build system done.
• [x] Better way for targets to select a cpu/arch
• [x] Patch elf
• [x] Build formats
• [x] Better ux for port writing
• [ ] Change all ports to work with the new build system (wip)
  • [ ] rp2xxx: find a way to build bootrom and also expose it so as to allow user targets to reference it
  • [x] lpc
• [ ] Change all examples to work with the new build system
• [ ] Final touches
  • [ ] Expose build tools (uf2, regz) from the microzig package
  • [ ] Add the package command back to the root build.zig
  • [ ] Make the user's app root package (instead of core/start.zig)