tsan: allow the Go runtime to return multiple stack frames for a single PC

This fix allows tsan to report stack traces correctly even in the
presence of mid-stack inlining by the Go compiler.

See https://go-review.googlesource.com/c/go/+/195781 for the Go runtime side of this change.

Author: randall77 (Keith Randall)
Reviewed: https://reviews.llvm.org/D67671
llvm-svn: 372205