LLVM 3.5: XFAIL the block case until the proposed Clang patch has been applied upstream.
TargetRegistry used to fall back to the 'cpp' target and this is
not the case anymore in LLVM 3.5. Unify the behavior by catching this
and assuming no target info is used in this case.
The pointer size should be 4B for a 32bit pointer.

Also initialize the size_t_width to avoid undefined behavior
in case of an NDEBUG build that does not get caught in
the assertion.