cmd/go: don't lose last flag from _cgo_flags

The quoting code that read _cgo_flags, currently only in the gccgo
version of cmd/go, was losing the last flag read from the file.

Fixes golang/go#23666

Change-Id: I6a45426bd28422461c3aeedfa68272a5ecae5ee5
Reviewed-on: https://go-review.googlesource.com/91655
Reviewed-by: Than McIntosh <thanm@google.com>
1 file changed