[release-branch.go1.12] cmd/link/internal/ld: bump macOS and macOS SDK version to 10.9
    
    Satisfies the Apple Notary.
    
    Fixes #30526
    
    Change-Id: I91cf2d706a3ebe79bafdb759a0d32266ed6b9096
    Reviewed-on: https://go-review.googlesource.com/c/go/+/175918
    Run-TryBot: Elias Naur <mail@eliasnaur.com>
    TryBot-Result: Gobot Gobot <gobot@golang.org>
    Reviewed-by: Keith Randall <khr@golang.org>
    Reviewed-on: https://go-review.googlesource.com/c/go/+/175919
    Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>