Fix linking issues on parallel builds

[flatmapthatshit]

While the Wiki often encourages parallel builds (e.g., with make -j4), tools/Makefile is not currently safe for parallel builds as it doesn't currently account for dependencies between programs.

E.g.:

• tabledesign → audiofile
• skyconv → n64graphics

More often than not, trying to compile tools with make -j4 will fail due to tabledesign finishing to compile before audiofile and then failing to link.

While this would ideally be solved by introducing separate rules per program accounting for dependencies, for now I'm forcing j1 for tools.

This fix was already merged upstream as part of PR sm64pc#512

[flatmapthatshit]

@AndratVA has already backported this fix to branch tester_rt64alpha (97fc00e)