Link thread-specific breakpoint test against libpthread


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@199448 91177308-0d34-0410-b5e6-96231b3b80d8
Undo r199448, already implemented in r199426



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@199449 91177308-0d34-0410-b5e6-96231b3b80d8