rtools43: Add version 4.3.5958.5975

[niheaven]

Move current main/rtools.json to versions/rtools43

• [x] I have read the Contributing Guide.

[github-actions[bot]]

All changes look good.

Wait for review from human collaborators.

rtools40

• [x] Description
• [x] License
• [x] Hashes

rtools42

• [x] Description
• [x] License
• [x] Hashes
• [x] Checkver
• [x] Autoupdate

rtools43

• [x] Description
• [x] License
• [x] Hashes
• [x] Checkver
• [x] Autoupdate