Bug#847822: qt3d-opensource-src: FTBFS on powerpc: __atomic_fetch_add_8 undefined

["Aaron M. Ucko" <ucko@debian.org>]

Source: qt3d-opensource-src
Version: 5.7.1~20161122+dfsg-2
Severity: important
Justification: fails to build from source

The latest build of qt3d-opensource-src for powerpc (admittedly not a
release architecture) failed:

  g++ -specs=/usr/share/dpkg/pie-link.specs -Wl,-z,relro -Wl,--as-needed -Wl,--no-undefined -Wl,--version-script,Qt3DCore.version -Wl,-O1 -Wl,--enable-new-dtags -shared -Wl,-soname,libQt53DCore.so.5 -o libQt53DCore.so.5.7.1 .obj/qtickclock.o ... obj/moc_propertychangehandler_p.o  -lQt5Gui -lQt5Network -lQt5Core -lpthread -lGL 
  .obj/qnodeid.o: In function `std::__atomic_base<unsigned long long>::fetch_add(unsigned long long, std::memory_order)':
  /usr/include/c++/6/bits/atomic_base.h:514: undefined reference to `__atomic_fetch_add_8'
  collect2: error: ld returned 1 exit status

Could you please take a look?  Linking against -latomic might help;
since you're already using -Wl,--as-needed, I expect you should even
be able to list that library unconditionally without getting a runtime
dependency on architectures that don't require it here.

Thanks!

-- 
Aaron M. Ucko, KB1CJC (amu at alum.mit.edu, ucko at debian.org)
http://www.mit.edu/~amu/ | http://stuff.mit.edu/cgi/finger/?amu@monk.mit.edu