cmd/link: revise test case to work on pre-10.14 macos

Rework this recently introduced test case to insure that it works with
older versions of the OS. It was using a new framework library not
available on pre-10.14 to trigger the weak symbol reference; switch to
using a new symbol from an existing library. Tested on MacOS 10.14 and
10.11.

Updates #32233.

Change-Id: I1fe2a9255fca46cb7cdf33ff7fed67bba86fdc22
Reviewed-on: https://go-review.googlesource.com/c/go/+/179837


Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>