Fix tracepoint.h multiple .o within module/core exec linkage bug

Fix tracepoint.h multiple .o within module/core exec linkage bug

We need all symbols looked up with dlopen to share the same linkage
property as the __tracepoint_registered variable (shared across .o in a
module/executable), otherwise only the first .o which runs its
constructor will have those defined.

Caused some tracepoints not to be traced in non-_LGPL_SOURCE
applications, due to the check:

if (!TP_RCU_LINK_TEST())   \
    return;

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