fix: build Python bindings with GCC10

fix: build Python bindings with GCC10

Disable -Wnull-dereference for native_bt.c

bt2/native_bt.c: In function ‘SWIG_Python_NewPointerObj.constprop’:
bt2/native_bt.c:2207:13: error: potential null pointer dereference [-Werror=null-dereference]
 2207 |   PyObject *newraw = data->newraw;
      |             ^~~~~~

Change-Id: I05db1c48304b1fbc715d273425e16d7605405b27
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/2852
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>
Tested-by: jenkins <jenkins@lttng.org>