[ThreadLauncher] Use mapWindowsError and LLDB_INVALID_HOST_THREAD
[ThreadLauncher] Use mapWindowsError and LLDB_INVALID_HOST_THREAD

Address post-commit feedback from Pavel and Jim.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@365403 91177308-0d34-0410-b5e6-96231b3b80d8

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