Description of problem:
With nunc-stans enabled ns-slapd crashes at startup on a machine with AMD Opteron 280 CPU:
==28269== Process terminating with default action of signal 4 (SIGILL): dumping core
==28269==  Illegal opcode at address 0x516F04A
==28269==    at 0x516F04A: abstraction_dcas (abstraction_dcas.c:179)
==28269==    by 0x516EF56: freelist_push (freelist_pop_push.c:84)
==28269==    by 0x516EC7C: freelist_new_elements (freelist_new.c:67)
==28269==    by 0x516ED40: freelist_new (freelist_new.c:31)
==28269==    by 0x516E48C: stack_new (stack_new.c:21)
==28269==    by 0x516CEB6: ns_thrpool_new (ns_thrpool.c:900)
==28269==    by 0x128EA9: slapd_daemon (daemon.c:1222)
==28269==    by 0x119ACB: main (main.c:1117)

nunc-stans uses libflds, which has this in the source:
src/abstraction/abstraction_dcas.c:183

   179	    __asm__ __volatile__
   180	    (
   181	      "xchg %%rsi, %%rbx;"  // swap RBI and RBX 
   182	      "lock;"               // make cmpxchg16b atomic
   183	      "cmpxchg16b %0;"      // cmpxchg16b sets ZF on success
   184	      "setz       %3;"      // if ZF set, set cas_result to 1
   185	      "xchg %%rbx, %%rsi;"  // re-swap RBI and RBX
   186	
   187	      // output
   188	      : "+m" (*(volatile atom_t (*)[2]) destination), "+a" (*compare), "+d" (*(compare+1)), "=q" (cas_result)
   189	
   190	      // input
   191	      : "S" (*exchange), "c" (*(exchange+1))
   192	
   193	      // clobbered
   194	      : "cc", "memory"
   195	    );

cmpxchg16b is not supported by some AMD proccessors
https://en.wikipedia.org/wiki/X86-64:
Early AMD64 processors (typically on Socket 939 and 940) lacked the CMPXCHG16B instruction, which is an extension of the CMPXCHG8B instruction present on most post-80486 processors. Similar to CMPXCHG8B, CMPXCHG16B allows for atomic operations on octal words. This is useful for parallel algorithms that use compare and swap on data larger than the size of a pointer, common in lock-free and wait-free algorithms. Without CMPXCHG16B one must use workarounds, such as a critical section or alternative lock-free approaches.

Version-Release number of selected component (if applicable):
389-ds-base-1.3.5.10-3.el7.x86_64

How reproducible:
always

Steps to Reproduce:
0. Use a machine with AMD Opteron 280
1. Enable nunc-stans
2. Start ns-slapd

Actual results:
Server crashes with SIGILL

Expected results:
Server should startup successfully.

Additional info:
processor	: 0
vendor_id	: AuthenticAMD
cpu family	: 15
model		: 33
model name	: Dual Core AMD Opteron(tm) Processor 280
stepping	: 2
microcode	: 0x4d
cpu MHz		: 2405.487
cache size	: 1024 KB
physical id	: 0
siblings	: 2
core id		: 0
cpu cores	: 2
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 1
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ht syscall nx mmxext fxsr_opt lm 3dnowext 3dnow art rep_good nopl extd_apicid pni lahf_lm cmp_legacy
bogomips	: 4810.97
TLB size	: 1024 4K pages
clflush size	: 64
cache_alignment	: 64
address sizes	: 40 bits physical, 48 bits virtual
power management: ts fid vid ttp