cmd/release: sanity check relocations before release
cmd/release: sanity check relocations before release

Updates golang/go#31293

Change-Id: I001e1f1518c302a9e8c49716d44860603fd5c28b
Reviewed-on: https://go-review.googlesource.com/c/build/+/171317
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/build,golang/build,golang/build,golang/build