[dev.regabi] cmd/compile: type check externdcl earlier
The next CL requires externdcl to be type checked earlier, but this
causes toolstash -cmp to complain because it causes src.PosBases to
get added in a different order. So split out into a separate CL.
Change-Id: Icab4eadd3fa8acffbd3e980bd8100924378351b3
Reviewed-on: https://go-review.googlesource.com/c/go/+/277732
Trust: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org> Reviewed-by: Russ Cox <rsc@golang.org>