This fixes an error on our Armv8 bot:
```
<...>/RemoteJITUtils.cpp:132:24: error: use of undeclared identifier 'DynamicThreadPoolTaskDispatcher'
132 | std::make_unique<DynamicThreadPoolTaskDispatcher>(std::nullopt),
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
```
These examples require LLVM_ENABLE_THREADS to be ON, and cannot run
otherwise. As a comment says elsewhere:
```
// Out of process mode using SimpleRemoteEPC depends on threads.
```
10767aad89