Up until now we rely on Thread objects and variants thereof to be allocated
on heap or embedded in another object that's zero'ed on initialization.
However sometimes it's convenient to be able to use them on stack as
will be the case when writting unit tests.
Initialize all relevant fields to allow them to be used on stack. While
at it, prefer C++11 initialization on Poller since it's only setting the
default (invalid) value.
Implementation of alloca() is very much architecture and compiler
dependent. Avoid the case in which it could return a non-aligned
pointer, which would mean Thread::_poison_stack() would do the wrong
thing.
../../libraries/AP_HAL_Linux/Thread.cpp: In member function ‘void Linux::Thread::_poison_stack()’:
../../libraries/AP_HAL_Linux/Thread.cpp:63:20: warning: declaration of ‘start’ shadows a member of 'this' [-Wshadow]
uint8_t *end, *start, *curr;
^
