cmd/link: keep go.buildinfo even with --gc-sections

cmd/link: keep go.buildinfo even with --gc-sections

If you use an external linker with --gc-sections, nothing refers
to .go.buildinfo, so the section is deleted, which in turns makes
'go version' fail on the binary. It is important for vulnerability
scanning and the like to be able to run 'go version' on any binary.

Fix this by inserting a reference to .go.buildinfo from the rodata
section, which will not be GC'ed.

Fixes #58222.

Change-Id: I1e13e9464acaf2f5cc5e0b70476fa52b43651123
Reviewed-on: https://go-review.googlesource.com/c/go/+/464435
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>