Currently I package 389-ds on Solaris-userland, where I build 389-ds for x86 and sparc. For the atmonic operations in slapi_counter.c I build with gcc.
Solaris GCC contains libatomic for i86 and sparc so that differentiation in configure.ac for Solaris Sparc or x86 is no longer necessary.
But to be sure, I would test these atmic operations in 389-ds.

Are there some testsuites or functions for slapi_counter?