Only use cpu_set_t on Linux

[riptl]

Issue number of the reported bug or feature request: #

Describe your changes

Makes TaskQueue::pinToCore a no-op on platforms that don't support cpu_set_t (i.e. non-Linux)

Testing performed

Compiled quantum on macOS.

Additional context

In the future, TaskQueue::pinToCore should be implemented on other platforms to improve performance.