This is a fixed-up version of D21612, to address failure identified post-commit.
Original commit description:
This patch implements the initialisation and patching routines for the XRay runtime, along with the necessary trampolines for function entry/exit handling. For now we only define the basic hooks for allowing an implementation to define a handler that gets run on function entry/exit. We expose a minimal API for controlling the behaviour of the runtime (patching, cleanup, and setting the handler to invoke when instrumenting).
- Gating XRay build to only Linux x86_64 and with the right dependencies in case it is the only library being built
- Including <cstddef> to fix std::size_t issue