Thread safety analysis: at a CFG join point between a block terminating in a

'continue' and another block, prefer the lockset from the other block, and
diagnose the 'continue' block as being the end of a loop.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149666 91177308-0d34-0410-b5e6-96231b3b80d8