s390x build failure

poking s390x build failure:

Executing gtest-nuxgraphics under dummy xserver results in illigel instructions:

# .libs/gtest-nuxgraphics
[==========] Running 9 tests from 2 test cases.
[----------] Global test environment set-up.
[----------] 8 tests from TestTextures
[ RUN ] TestTextures.TestTextureSizes
Illegal instruction (core dumped)

Program received signal SIGILL, Illegal instruction.
0x000003fffdf2e53a in nux::NThreadSafeCounter::Increment (this=0x3fffdf53f2e <nux::SystemStart()::StaticBuffer+200>) at ThreadGNU.cpp:31
31 return __sync_add_and_fetch (&m_Counter, 1);
(gdb) backtrace full
#0 0x000003fffdf2e53a in nux::NThreadSafeCounter::Increment (this=0x3fffdf53f2e <nux::SystemStart()::StaticBuffer+200>) at ThreadGNU.cpp:31
No locals.

But there is nothing special in ThreadGNU.cpp:31 it simply does:

  int NThreadSafeCounter::Increment()
  {
    return __sync_add_and_fetch (&m_Counter, 1);
  }