[AIX] Add threadId and use nanosecond timestamp in sinit/sterm symbols

With ThinLTO, when compiling SPEC 2017 omnetpp_r with -threads=4, two
small modules can end up with the same timestamp in their sinit symbols
when calculating time in seconds, creating duplicate definitions.

This patch uses a timestamp in nanoseconds.
Because the race can be between threads, embed the thread ID as well.

Reviewed By: xingxue, daltenty

Differential Revision: https://reviews.llvm.org/D159319