Mark as BROKEN on powerpc64.

The complete error message:

1. In file included from ./../../src/conc/AtomicPtr.h:30,
2. from ./../../src/conc/CellPool.h:30,
3. from ./../../src/conc/ObjPool.h:44,
4. from ../../src/fmtc/Bitdepth.h:30,
5. from ../../src/main.cpp:18:
6. ./../../src/conc/def.h:45:3: error: #error

Approved by: portmgr (tier-2 blanket)