[lld][WebAssembly] Fix use of undefined funcs under --warn-unresolved-symbols (#78643)

When undefined functions exist in the final link we need to create
stub functions (otherwise direct calls to those functions could
not be generated).  We were creating those stub when
`--unresolved-symbols=ignore-all` was passed but overlooked the fact
that `--warn-unresolved-symbols` essentially has the same effect (i.e.
undefined function can exist in the final link).

Fixes: #53987

Author: sbc100

lld/test/wasm/unresolved-symbols.s

@@ -18,10 +18,15 @@
 # RUN:   FileCheck -check-prefix=ERR1 %s
 
 ## Ignore all should not produce error and should not produce
-# any imports.  It should create a stub function in the place of the missing
-# function symbol.
+## any imports.  It should create a stub function in the place of the missing
+## function symbol.
 # RUN: wasm-ld %t1.o -o %t2.wasm --unresolved-symbols=ignore-all
 # RUN: obj2yaml %t2.wasm | FileCheck -check-prefix=IGNORE %s
+
+## --warn-unresolved-symbols should behave the same
+# RUN: wasm-ld %t1.o -o %t2.wasm --warn-unresolved-symbols
+# RUN: obj2yaml %t2.wasm | FileCheck -check-prefix=IGNORE %s
+
 # IGNORE-NOT: - Type:            IMPORT
 # IGNORE-NOT: - Type:            ELEM
 #
@@ -52,10 +57,10 @@
 # IGNORE-NEXT:      - Index:           3
 # IGNORE-NEXT:        Name:            get_func_addr
 
-## --import-undefined should handle unresolved funtions symbols
-# by importing them but still report errors/warning for missing data symbols.
-# `--allow-undefined` should behave like `--import-undefined` +
-# `--unresolve-symbols=ignore`
+## --import-undefined should handle unresolved functions symbols
+## by importing them but still report errors/warning for missing data symbols.
+## `--allow-undefined` should behave like `--import-undefined` +
+## `--unresolve-symbols=ignore`
 # RUN: wasm-ld %t1.o -o %t3.wasm --import-undefined --unresolved-symbols=ignore-all
 # RUN: obj2yaml %t3.wasm | FileCheck -check-prefix=IMPORT %s
 #      IMPORT:  - Type:            IMPORT

lld/wasm/Relocations.cpp

@@ -54,21 +54,22 @@ static void reportUndefined(Symbol *sym) {
     case UnresolvedPolicy::Ignore:
       LLVM_DEBUG(dbgs() << "ignoring undefined symbol: " + toString(*sym) +
                                "\n");
-      if (!config->importUndefined) {
-        if (auto *f = dyn_cast<UndefinedFunction>(sym)) {
-          if (!f->stubFunction) {
-            f->stubFunction = symtab->createUndefinedStub(*f->getSignature());
-            f->stubFunction->markLive();
-            // Mark the function itself as a stub which prevents it from being
-            // assigned a table entry.
-            f->isStub = true;
-          }
-        }
-      }
       break;
     case UnresolvedPolicy::ImportDynamic:
       break;
     }
+
+    if (auto *f = dyn_cast<UndefinedFunction>(sym)) {
+      if (!f->stubFunction &&
+          config->unresolvedSymbols != UnresolvedPolicy::ImportDynamic &&
+          !config->importUndefined) {
+        f->stubFunction = symtab->createUndefinedStub(*f->getSignature());
+        f->stubFunction->markLive();
+        // Mark the function itself as a stub which prevents it from being
+        // assigned a table entry.
+        f->isStub = true;
+      }
+    }
   }
 }