[NFC][compiler-rt][hwasan] Move hwasanThreadList().CreateCurrentThread() into InitThreads

Once D104553 lands, CreateCurrentThread will be able to accept optional
parameters for initializing the hwasan thread object. On fuchsia, we can get
stack info in the platform-specific InitThreads and pass it through
CreateCurrentThread. On linux, this is a no-op.

Differential Revision: https://reviews.llvm.org/D104561