Add tests that invoke a linker which uses generated linker scripts from slinky

[AngheloAlf]

Have dummy projects (with dummy C and asm files) that get built and linked using linker scripts generated by slinky.

Would be nice a few multiple projects that aim to represent multiple kinds of projects/platforms/variants, so we don't miss anything. Including but not limited to:

• [ ] N64
  • [ ] IDO
  • [ ] KMC
  • [ ] EGCS
  • [ ] Out of normal RAM segments
  • [ ] Multiple overlays
  • [ ] Shared vram overlays
• [ ] PSX
  • [ ] PSX-EXE
  • [ ] Overlays (or whatever they are called)
  • [ ] No use of $gp register (-G0)
  • [ ] Hardcode the $gp register in the yaml
  • [ ] Shiftable $gp register
• [ ] PS2
  • [ ] idk
• [ ] GC / Wii
  • [ ] idk

Make sure the produced binary and mapfile is still the same as expected