objects used to provide per-thread storage in the RPC code. Almost all
of these used double-checking with a dedicated mutex (tsd_lock) to do this
before. However, that is not always safe with more relaxed memory orders.
There were also other bugs, such as one in __rpc_createrr() that caused a
new key to be allocated each time __rpc_createrr() was invoked.
PR: threads/144558
Reported by: Sam Robb samrobb of averesystems com (key leak)
MFC after: 1 week
