Enable/disable entanglement detection at compile-time in the runtime system

[shwestrick]

Compile time argument -detect-entanglement true now enables DETECT_ENTANGLEMENT preprocessor flag in the runtime system, letting us selectively disable entanglement detection code.

This is now used for the following, which are only enabled when -detect-entanglement true is passed at compile time.

1. With entanglement detection on, threads additionally store a list of ancestor synchronization depths (for the DePa algorithm).
2. With entanglement detection on, the scheduler reverts to sequential at large depths, to ensure our initial implementation of DePa doesn't need large strand identifiers.

This patch also removes the old LTO runtime, which we don't use anymore.