Cygwin: pipe: Introduce temporary query_hdl.
- The commit
f79a4611 introduced query_hdl, which is the read pipe
handle kept in the write pipe instance in order to determine if
the pipe is ready to write in select(). This implementation has
a potential risk that the write side fails to detect the closure
of the read side if more than one writer exists and one of them
is a non-cygwin process.
With this patch, the strategy of commit
f79a4611 is used only if
the process is running as a service. For a normal process,
instead of keeping query_hdl in the write pipe instance, it is
retrieved temporarily when select() is called. Actually, we
want to use tenporary query_hdl for all processes, however, it
does not work for service processes due to OpenProcess()
failure.