Add abbreviated name for Debugger::EventHandlerThread.
Add abbreviated name for Debugger::EventHandlerThread.

On OS's where thread names are limited to 16 bytes, the full name was truncated to not very meaningful "r.event-handler".

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@336991 91177308-0d34-0410-b5e6-96231b3b80d8

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