[test] t/dynoplibs/debug.t %p on cygwin/newlib has no 0x

no leading 0x for %p. we use now fprintf directly to stress the GC less
unify platform encoding.c

Closes GH #1120.
Get support for other platform encodings for free.
trace: less GC stress for trace
temp: expand 2 POINTER_ARRAY_ITER macros

for easier debugging