Fix =thread-exited message (MI)
Fix =thread-exited message (MI)

Summary:
This patch includes:
# Fix invalid thread id in =thread-exited message
# Remove invalid threads from cache

All tests pass on OS X.

Test Plan:
now
```
=thread-exited,id="3",group-id="i1"
=thread-exited,id="4",group-id="i1"
=thread-exited,id="5",group-id="i1"
```

was
```
=thread-exited,id="4294967295",group-id="i1"
=thread-exited,id="4294967295",group-id="i1"
...
=thread-exited,id="4294967295",group-id="i1"
=thread-exited,id="4294967295",group-id="i1"
```

Reviewers: abidh

Reviewed By: abidh

Subscribers: lldb-commits, abidh

Differential Revision: http://reviews.llvm.org/D8603

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@233256 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb