libdispatch bindings on 32-bit

The libdispatch bindings will crash when running with 32-bit code, or using an older deployment target.

Think about providing bindings that opt out of OS_OBJECT_USE_OBJC to be able to support these targets.

My gut feeling is that this isn't worth the trouble.

The alternative is only needed for 32-bit on macOS 10.11 or earlier.