lang/retro12: Update to 2018.8

Also:

• Fix the order of variables.
• Set USES=shebangfix for the rre interpreter.

PR: 232885
Submitted by: w.schwarzenfeld@utanet.at
Reviewed by: krion, mat ndowens_yahoo.com
Approved by: mat (mentor)
Differential Revision: https://reviews.freebsd.org/D17830