Prevent occasional infinite loop when unwinding stack on ARM

If PC didn't change from the previous unwound frame and we made a guess that SP is a frame pointer (last resort), we're now in an infinite loop creating frames with SP increasing by cache->framesize, but in fact the
loop is unwinding a single stack frame over and over. Upon detecting this condition use stack pointer from the current frame to create an already existing id for this frame in order to force breaking the loop.

Tested with crashes in harbour-netradar and harbour-reversi.