[Sanitizer] Turn GetStackTrace() into StackTrace::Unwind()

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@192533 91177308-0d34-0410-b5e6-96231b3b80d8
[Sanitizer] Remove StackTrace::max_depth field

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@192534 91177308-0d34-0410-b5e6-96231b3b80d8