cmd/link: linkname directive on userspace variable can override runtime variable [1.23 backport]

[gopherbot]

@cherrymui requested issue #72032 to be considered for backport to the next 1.23 minor release.

@gopherbot please backport this to previous releases. This is a regression that breaks some existing uses of linkname. Thanks.

[cagedmantis]

This backport request has been approved. We should keep compatibility with previous versions.

[gopherbot]

Change https://go.dev/cl/662355 mentions this issue: [release-branch.go1.23] cmd/link: choose one with larger size for duplicated BSS symbols

[gopherbot]

Closed by merging CL 662355 (commit 96537d5) to release-branch.go1.23.