Fix: work-around gcc optimisation oddness on 32-bit powerpc

Deal with gcc O1 optimisation issues with weak hidden symbols. gcc 4.8
and prior does not have the same behavior for symbol scoping on 32-bit
powerpc depending on the object size: symbols for objects of 8 bytes or
less have the same address throughout a module, whereas they have
different addresses between compile units for objects larger than 8
bytes. Add this pointer indirection to ensure that the symbol scoping
match that of the other weak hidden symbols found in tracepoint.h.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>