[release-branch.go1.18] cmd/link: preserve symbol attributes when cloning to external
[release-branch.go1.18] cmd/link: preserve symbol attributes when cloning to external

There are some symbol attributes that are encoded in the object
file. Currently, they are lost when cloning a symbol to external.
Copy them over.

Also delete CopyAttributes as it is no longer called anywhere.

For #53107. Backporting this CL as the fix of #53107 depends on
it.

Change-Id: I1497e3223a641704bf35aa3e904dd0eda2f8ec3e
Reviewed-on: https://go-review.googlesource.com/c/go/+/400574
Run-TryBot: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>
(cherry picked from commit df08c9a82152fd6f2b2811db03b40fea8b6e5e9e)
Reviewed-on: https://go-review.googlesource.com/c/go/+/408820

cloudflare/go,cloudflare/go,cloudflare/go,cloudflare/go,cloudflare/go,cloudflare/go,cloudflare/go,cloudflare/go