cad/nvc: Update 1.17.1 => 1.18.0

[alven]

Summary

Changelogs:

• https://www.nickg.me.uk/nvc/news.html#version-1.18.0---2025-09-28

• Switch MASTER_SITES to upstream official site, add WWW for it
• Mark ONLY_FOR_ARCHS= aarch64 amd64 as the only supported by upstream for now:
  
  https://github.com/nickg/nvc/blob/14f8f7c4a1733fc39b35799e8ae0328e91d1ae0f/src/jit/jit-code.c#L854

• Remove workarounds for issues closed in upstream
• Pet portclippy(1) and portfmt(1)

Test Plan

For every {amd64} × {14.3, 13.5}:

• Successful poudriere testport
• Successful run-testing

[yuri]

Approved.

Thanks,
Yuri