build: allow building with dtrace on osx
dtrace: pass more arguments to probes

OSX and other DTrace implementations don't support dereferencing
structs in probes. To accomodate that pass members from the struct as
arguments so that DTrace is useful on those systems.
dtrace: actually use the _handle.fd value

When using the DTrace/systemtap subsystems it would be helpful to
actually have an fd associated with the requests and responses.
dtrace: check if _handle property is set

Check that _handle is an object before trying to read its `fd`
property, avoids bogus values.
etw: update prototypes to match dtrace provider

The DTrace probes were updated to accomodate platforms that can't
handle structs, update the prototypes for ETW but it's not necessary
to do anything with the new arguments as it's redundant information.