cmd/go/internal/load,cmd/link/internal/ld: use objabi.LookupPkgSpecial(pkg).Runtime
As suggested by Michael in CL 655515.
Change-Id: Idf0b879287bd777d03443aebc7351fcb0d724885
GitHub-Last-Rev:
58eda020f5310f873674f56903facec4f212d6c0
GitHub-Pull-Request: golang/go#72806
Reviewed-on: https://go-review.googlesource.com/c/go/+/656856
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>