Add Go buildids into a custom wasm section ("go.buildid", arbitrarily)
early in the wasm module, right after the magic & version.

Fixes #25910

Change-Id: If3f7cb267bf8c7beb6fa8d8b7a4829419720bbd8
Reviewed-on: https://go-review.googlesource.com/119175
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>