sysutils/jdupes: Update to 1.21.0

Use xxHash from ports instead of bundled version
Strip hardcoded optimization and -g
Remove hardcoded GCC version check

Changelog: https://github.com/jbruchon/jdupes/releases/tag/v1.21.0

PR: 267073
Reviewed by: Thomas Hurst <tom@hur.st> (maintainer)