Various TARGETs create new flavors of LINT for testing and do so differently based on whether or not a single common LINT is going to be sticking around. amd64/i386 are currently the only TARGETs that clean up the extras upon make clean.
Make things a little more consistent by defining an EXTRALINT at the top that defines these other LINTs that will need to be cleaned up later. These will also be automatically generated from the full contents of LINT and later parts of the LINT target can optionally append to these extra lints as needed, which has the benefit of making later additions trivially audited as nothing should be overwriting the contents of extra LINTs.
The major change here is for the x86 flavors of LINT, as they previously existed as "include LINT" and then the additions. These will now be a full copy of the base LINT, which is presumably not really all that much of an issue as we don't necessarily support modifying LINT as opposed to regenerating from NOTES.