[TSan] Use StackTrace from sanitizer_common where applicable

Summary:
This change removes `__tsan::StackTrace` class. There are
now three alternatives:
  # Lightweight `__sanitizer::StackTrace`, which doesn't own a buffer
  of PCs. It is used in functions that need stack traces in read-only
  mode, and helps to prevent unnecessary allocations/copies (e.g.
  for StackTraces fetched from StackDepot).
  # `__sanitizer::BufferedStackTrace`, which stores buffer of PCs in
  a constant array. It is used in TraceHeader (non-Go version)
  # `__tsan::VarSizeStackTrace`, which owns buffer of PCs, dynamically
  allocated via TSan internal allocator.

Test Plan: compiler-rt test suite

Reviewers: dvyukov, kcc

Reviewed By: kcc

Subscribers: llvm-commits, kcc

Differential Revision: http://reviews.llvm.org/D6004

llvm-svn: 221194