devel/vectorscan: Fix various style issues.
- Use DISTVERSION instead of PORTVERSION
- Fix variable ordering
- Fix compiler requirement: compiler:c++11-lib -> compiler:c++17-lang
- Respect CFLAGS: patch cmake/cflags-generic.cmake to not hardcode -O3, and patch CMakeLists.txt to not strip -O from config-specific flags
- Add OPTIMIZED_CFLAGS option (default on) to restore -O3 for performance, letting users opt out while matching upstream intent
- Fix options ordering: OPTIONS_DEFAULT before OPTIONS_RADIO, descriptions and helpers in canonical order
Reported by: diizzy