The DIEs for global variables were all assigned to the first emitted
compile unit in debug_info, regardless of what it was. Move them
instead to their respective compile units.

Change-Id: If794fa0ba4702f5b959c6e8c16119b16e7ecf6d8
Reviewed-on: https://go-review.googlesource.com/137235Reviewed-by: Than McIntosh <thanm@google.com>