don't call it according to the runtime specification and especially
WRT to gp this can cause trouble. The gcc 3.3.1 import broke the
ia64 runtime because the compiler saved gp prior to us being able
to set it properly. Restoring gp after the calls would then invalidate
gp and cause segmentation faults later on.
By rewriting _start() as an assembly function, we also avoided even
more gcc dependences, by trying to use gcc specific features to work
around the problem.
This version of _start() does not reference _DYNAMIC. We register the
cleanup function when it's a non-NULL pointer. The kernel will always
pass a NULL pointer and dynamic linkers may pass a non-NULL pointer.
The machine independent code to set __progname now unfortunately is
written in assembly. So be it.
