Fix unsymbolized stack history printing.

Summary:
When symbols are unavailable, the current code prints
  sp: ... pc: ... (null) (null)
instead of module name + offset.

Change the output to include module name and offset, and also to match
the regular sanitizer stack trace format so that it is recognized by
symbolize.py out of the box.

Reviewers: kcc, pcc

Subscribers: kubamracek, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58267

llvm-svn: 354157