ldso: turn on object mapping message by default

Showing the object base map address always eases debugging. If Genode
is build in release mode, fall back to normal dbg definition.
dde_rump: update rumpkernel to b61e654193c2d
dde_rump: make size_t non ambigious
dde_rump: remove local Elf struct typedef
dde_rump: initial impl of rumpuser_thread_exit [WIP]