[TaskLocals] Avoid use of `defer` in back deployed functions in the standard library.
Older versions of the 5.8 compiler have a bug when generating SIL for functions with `@_backDeploy` containing defer blocks (https://github.com/apple/swift/pull/62444) and for now we need the standard library interface to be compatible with those older compilers.
Resolves rdar://104045168