Move lttng wrappers into own module

Currently, we only pull the wrapper symbols into a single sub-module,
either:

lttng-tracer.o:
  - wrapper/random.o
  - wrapper/trace-clock.o
  - wrapper/page_alloc.o

or

lttng-statedump.o:
  - wrapper/irqdesc.o
  - wrapper/fdtable.o

Because lttng-tracer depends on lttng-statedump, we cannot just put all
wrappers into lttng-tracer.o, because it would create a circular
dependency. This will be an issue if we introduce common wrappers which
are used in both lttng-tracer.o and in lttng-statedump.o.

Introduce a new lttng-wrapper.o to contain all wrapper symbols for all
lttng modules.

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