[lldb-server] Add unnamed pipe support to PipeWindows

Summary:
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

llvm-svn: 350784