[XRay][compiler-rt] Handle tail-call exits in the XRay runtime

Summary:
This change starts differentiating tail exits from normal exits. We also
increase the version number of the "naive" log to version 2, which will
be the starting version where these records start appearing. In FDR mode
we treat the tail exits as normal exits, and are thus subject to the
same treatment with regard to record unwriting.

Updating the version number is important to signal older builds of the
llvm-xray tool that do not deal with the tail exit records must fail
early (and that users should only use the llvm-xray tool built after
the support for tail exits to get accurate handling of these records).

Depends on D37964.

Reviewers: kpw, pelikan

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D37965

llvm-svn: 313515