Adding optional debug flags to linux makefile so that
swt custom native glue code can be debugged when required.

It's not trivially obvious how to set the flags for
debugging without these, as "NO_STRIP" doesn't come
to mind when trying to setup swt debugging.

Change-Id: Id97cd529a85ecad56ee15bfae5448f8364627677
Signed-off-by: Leo Ufimtsev <lufimtse@redhat.com>