misc/bb: patch properly
- remove REGPARM entirely, it doesn't do any good these days and blocks portability
- remove use of gcc, no longer needed
- patch some portability issues
MFH: 2026Q1
Sponsored by: Raptor Computing Systems, LLC
(cherry picked from commit 5cc28c8ebd451e1a34fed73e0998d42d5c5ad627)