On platforms where pointers are larger than 64-bits, struct statsblob
may be harmlessly padded out such that opaque[] always has some included
space. Make the assertion more general by compating to the offset of
opaque rather than the size of sizeof(struct statsblob).
truss: centralize pointer-constructing casts.
Arguments pointers are passed around as integrer types and need
to be converted to pointers when performing ptrace IO operations such as
in get_struct(). Move the casts into get_struct() and friends and take
a uintptr_t argument rather than a void *.
Add a print_pointer function that takes a uintptr_t and uses a single
case plus "%p" to print pointers.