Fix workgroup tests that declared an incompatible printf().
LLVM 3.4: all except 'block', 'bfs/PB', and 'lbm/PB' now pass.
Clang 3.4 adds a new diagnostics that correctly detects a typo in a macrodefine in lbm/PB. Ignore it.
Marked XFAILs (two of them) for LLVM 3.4. Now the suite passes for LLVM 3.4.