[lldb-server] Add unnamed pipe support to PipeWindows
This adds unnamed pipe support in PipeWindows to support communication between a debug server and child process.
Modify PipeWindows::CreateNew to support the creation of an unnamed pipe.
Rename the previous method that created a named pipe to PipeWindows::CreateNewNamed.
Reviewers: zturner, llvm-commits
Reviewed By: zturner
Subscribers: Hui, labath, lldb-commits
Differential Revision: https://reviews.llvm.org/D56234