When generating an abstract function DIE, call objabi.PathToPrefix on
the import path so as to be consistent with how the linker handles
import paths. This is intended to resolve another problem with DWARF
inline info generation in which there are multiple inconsistent
versions of an abstract function DIE for a function whose package path
is rewritten/canonicalized by objabi.PathToPrefix.

Fixes #26237

Change-Id: I4b64c090ae43a1ad87f47587a1a71f19bc5fc8e8
Reviewed-on: https://go-review.googlesource.com/123036
Run-TryBot: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>