Widen psaddr_t from uintptr_t to uint64_t. This results in an

Widen psaddr_t from uintptr_t to uint64_t.  This results in an
ABI change on ILP32 platforms and relating to events.  However
it's harmless on little-endian ILP32 platforms in the sense
that it doesn't cause breakages.  Old ILP32 thread libraries
write a 32-bit th_p and new thread libraries write a 64-bit
th_p.  But due to the fact that we have an unused 32-bit data
field right after th_p and that field is always initialized to
zero, little-endian ILP32 machines effectively have a valid
64-bit th_p by accident. Likewise for new thread libraries and
old libthread_db: little endian ILP32 is unaffected.

At this time we don't support big-endian threaded applications
in GDB, so the breakage for the ILP32 case goes unnoticed.