The call "poptemp(t, order)" at line 906 should match up with the
assignment "t := marktemp(order)" at line 770, so use a new temporary
variable for stripping the ODCL nodes from a "case x := <-ch" node's
Ninit list.

Fixes #13469.
Passes toolstash/buildall.

Change-Id: Ia7eabd40c79cfdcb83df00b6fbd0954e0c44c5c7
Reviewed-on: https://go-review.googlesource.com/17393
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>