rts/PEi386: Fix handling of weak symbols

Previously we would flag the symbol as weak but failed
to set its address, which must be computed from an "auxiliary"
symbol entry the follows the weak symbol.

Fixes #21556.

(cherry picked from commit 53b3fa1c)

rts/linker/PEi386.c

@@ -1657,6 +1657,13 @@ ocGetNames_PEi386 ( ObjectCode* oc )
       }
       else if (symStorageClass == IMAGE_SYM_CLASS_WEAK_EXTERNAL) {
           isWeak = true;
+          CHECK(getSymNumberOfAuxSymbols (info, sym) == 1);
+          CHECK(symValue == 0);
+          COFF_symbol_aux_weak_external *aux = (COFF_symbol_aux_weak_external *) (sym+1);
+          COFF_symbol* targetSym = &oc->info->symbols[aux->TagIndex];
+          int32_t targetSecNumber = getSymSectionNumber (info, targetSym);
+          Section *targetSection = targetSecNumber > 0 ? &oc->sections[targetSecNumber-1] : NULL;
+          addr = (SymbolAddr*) ((size_t) targetSection->start + getSymValue(info, targetSym));
       }
       else if (  secNumber == IMAGE_SYM_UNDEFINED && symValue > 0) {
          /* This symbol isn't in any section at all, ie, global bss.

rts/linker/PEi386.h

@@ -117,6 +117,12 @@ union _COFF_symbol {
     COFF_symbol_ex ex;
 } COFF_symbol;
 
+typedef
+struct {
+    uint32_t TagIndex;
+    uint32_t Characteristics;
+} COFF_symbol_aux_weak_external;
+
 /* A record for storing handles into DLLs. */
 typedef
 struct _OpenedDLL {

testsuite/tests/ghci/linking/all.T

@@ -42,8 +42,6 @@ test('ghcilink006',
 
 test('T3333',
      [unless(doing_ghci, skip),
-      unless(opsys('linux') or opsys('darwin') or ghc_dynamic(),
-             expect_broken(3333)),
       when(unregisterised(), fragile(17018))],
      makefile_test, ['T3333'])