This change allows the XRay basic (naive) mode logging implementation to
start writing the payload entries through the arg1 logging handler. This
implementation writes out the records that the llvm-xray tool and the
trace reader library will start processing in D38550.
This introduces a new payload record type which logs the data through
the in-memory buffer. It uses the same size/alignment that the normal
XRay record entries use. We use a new record type to indicate these new
entries, so that the trace reader library in LLVM can start reading
Depends on D38550.