devel/re2c: Update to 4.1

• Simplify port Makefile, build everything in one go
• Adjust port Makefile to closer follow Porters Handbook

Changelog: https://re2c.org/releases/release_notes.html#release-4-1

PR: 285457
Reviewed by: Corey Halpin <chalpin@cs.wisc.edu> (maintainer)
Tested by: Corey Halpin <chalpin@cs.wisc.edu> (maintainer)