We use one bit of the third reserved swift private tls key.
Also move the functionality into a separate static archive that is
always linked dependent on deployment target.
The mapping of the return value of the `FlsAlloc` was flipped resulting
in the failure of the TLS key creation. The test suite would fail to
generate the TLS key resulting in failures.
Fix syntactic issues in the swift runtime build from the recent TLS changes.
Move the helper definitions into the TLS stubs rather than emitting them
everywhere. This allows the runtime to build again on Windows.
