for gcc >= 2.5 and no-ops for gcc >= 2.6. Converted to use __dead2
or __pure2 where it wasn't already done, except in math.h where use
of __pure was mostly wrong.
understand why it can become a null pointer under some circumstances,
but i've got a pile of tapes where this happens, and running it thru a
debugger proved that simply ending the loop in this case did the right
thing.
Anyway, it cannot make it worse than now, where restore kills itself
with "Memory fault".
