[TSan][libdispatch] Fix compilation error on Linux

The interceptor for the block variants of the API references the
function versions (via `REAL(name##_f)`).  On Linux, this accesses the
underlying "real pointer", defined by the interceptor macro.  So we need
to declare interceptors in the right order to avoid undefined symbol
compiler error:
```
error: no member named 'real_dispatch_async_and_wait_f' in namespace '__tsan::__interception'
```

rdar://68181542