Userspace RCU

It appears gcc-14 (or maybe just Debian's gcc-14) defaults to -Werror=implicit-function-declaration. Building programs with liburcu 0.15.0 fails with that gcc due to:

In file included from /usr/include/powerpc64le-linux-gnu/urcu/uatomic/ppc.h:228,
                 from /usr/include/powerpc64le-linux-gnu/urcu/uatomic.h:73,
                 from lock.h:5,
                 from lock.c:1:
/usr/include/powerpc64le-linux-gnu/urcu/uatomic/generic.h: In function ‘_uatomic_and’:
/usr/include/powerpc64le-linux-gnu/urcu/uatomic/generic.h:422:24: error: implicit declaration of function ‘abort’ [-Wimplicit-function-declaration]
  422 |                 oldt = uatomic_read((uint32_t *) addr);
      |                        ^~~~~~~~~~~~
/usr/include/powerpc64le-linux-gnu/urcu/uatomic/generic.h:1:1: note: include ‘<stdlib.h>’ or provide a declaration of ‘abort’
  +++ |+#include <stdlib.h>
    1 | // SPDX-FileCopyrightText: 1991-1994 by Xerox Corporation.  All rights reserved.

Would be nice if this could be fixed upstream.

Debian bug: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1097513

Thanks!