debug/buildinfo: check pointer size on buildinfo.Read

debug/buildinfo: check pointer size on buildinfo.Read

Previous implementation has a check on pointer size but only if ptrSize
is 4. but it does not check on ptrSize 8 causing the panic on read for
some inputs.

The explicit check for pointer size 8 is added and error is returned if
ptrSize is not 4 and not 8.

Fixes #57002

Change-Id: Id51de72bdef4da9955d086bfc2a5d735678ee2ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/454616
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>