sysutils/liburcu: update to 0.15.1 release (+)

This update unbreak BIND 9.20 builds on aarch64

Changelog:
2025-02-18 [*] Userspace RCU 0.15.1

• uatomic/generic: Add missing #include <stdlib.h>
• docs: Clarify that make is required to build the project
• fix: add missing SPDX headers to urcu/uatomic/api.h
• compiler.h: Remove caa_unqual_scalar_typeof

PR: 286498
Approved by: maintainer timeout, 2mo+