fix(elf): follow loader version index precedence

VERDEF entries replace VERNEED names for shared indices, matching glibc lookup behavior.

docs/binary-diagnostics.md

@@ -334,11 +334,12 @@ count and SHA-256.
   `.gnu.version_r`, and the `hidden` flag from `.gnu.version`. `"unknown"`
   means the symbol-version table could not be read. A hidden version is not
   the default version that a by-name `dlsym` lookup selects.
+  Definition names take precedence when both tables name the same index.
 
 Unreadable names, out-of-range name ordinals and unreadable forwarders are
 listed in `issues`, their entries are not reported, and coverage is `partial`.
 Unresolved symbol versions keep their rows: the version name is null when no
-unambiguous definition or requirement names the index, and `version` is
+definition or requirement names the index, and `version` is
 `"unknown"` when the version table cannot be read; coverage is likewise
 `partial`. A dynamic symbol table without its null entry is malformed. An ELF
 without section headers is `unsupported`: