x11/i3lock-color: Update 2.13.c.4 => 2.13.c.5, fix build

Changelog:
github.com/Raymo111/i3lock-color/releases/tag/2.13.c.5

Port changes:

• Remove unneeded GNU_CONFIGURE_MANPREFIX.
• Fix build by removing redundant STRIP_CMD.
• Switch from GCC to system clang.
• Add bash completions for bash and zsh.
• Pet portfmt.

PR: 294968
Reported by: Dan Kotowski
Approved by: vvd (co-mentor)
Co-authored-by: Vladimir Druzenko <vvd@FreeBSD.org>
MFH: 2026Q2