win32: Switch thread abstraction to us TLS variable internally We already depend on working __thread support for coroutines, so this complication here is no longer needed. Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>