[lld][WebAssembly] Fix non-pie dynamic-linking executable

The commit 22b7b84
made the symbols provided by shared libraries "defined",
and thus effectively made it impossible to generate non-pie
dynamically linked executables using --unresolved-symbols=import-dynamic.

This commit, based on #109249,
fixes it by checking sym->isShared() explictly.
(as a bonus, you don't need to rely on --unresolved-symbols=import-dynamic
anymore.)

Fixes #107387

Author: yamt

lld/wasm/Relocations.cpp

@@ -146,7 +146,8 @@ void scanRelocations(InputChunk *chunk) {
 
     if (ctx.isPic ||
         (sym->isUndefined() &&
-         config->unresolvedSymbols == UnresolvedPolicy::ImportDynamic)) {
+         config->unresolvedSymbols == UnresolvedPolicy::ImportDynamic) ||
+        sym->isShared()) {
       switch (reloc.Type) {
       case R_WASM_TABLE_INDEX_SLEB:
       case R_WASM_TABLE_INDEX_SLEB64: