Give preempting symbols precedence over linker script

[pcc]

LGTM

I wonder whether we need Symbol::ExportDynamic any more now.

ELF/SymbolTable.cpp

void SymbolTable<ELFT>::addShared(SharedFile<ELFT> *F, StringRef Name,
   // DSO symbols do not affect visibility in the output, so we pass STV_DEFAULT
   // as the visibility, which will leave the visibility in the symbol table
   // unchanged.
   Symbol *S;
   bool WasInserted;
   std::tie(S, WasInserted) =
       insert(Name, Sym.getType(), STV_DEFAULT, /*CanOmitFromDynSym*/ true, F);
   // Make sure we preempt DSO symbols with default visibility.
-  if (Sym.getVisibility() == STV_DEFAULT)
+  if (Sym.getVisibility() == STV_DEFAULT) {
     S->ExportDynamic = true;
+    // Exporting preempting symbols takes precedence over linker scripts.
+    if (S->VersionId == VER_NDX_LOCAL)
+      S->VersionId = VER_NDX_GLOBAL;
+  }
   if (WasInserted || isa<Undefined>(S->body())) {
     replaceBody<SharedSymbol<ELFT>>(S, F, Name, Sym, Verdef);
     if (!S->isWeak())
       F->IsUsed = true;
   }
 }
 
 template <class ELFT>

test/ELF/gc-sections-shared.s

 # CHECK-NEXT:     Value:
 # CHECK-NEXT:     Size:
 # CHECK-NEXT:     Binding: Local
 # CHECK-NEXT:     Type:
 # CHECK-NEXT:     Other:
 # CHECK-NEXT:     Section: Undefined (0x0)
 # CHECK-NEXT:   }
 # CHECK-NEXT:   Symbol {
+# CHECK-NEXT:     Name: bar
+# CHECK-NEXT:     Value:
+# CHECK-NEXT:     Size:
+# CHECK-NEXT:     Binding: Global
+# CHECK-NEXT:     Type:
+# CHECK-NEXT:     Other:
+# CHECK-NEXT:     Section: .text
+# CHECK-NEXT:   }
+# CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name: bar2
 # CHECK-NEXT:     Value:
 # CHECK-NEXT:     Size:
 # CHECK-NEXT:     Binding: Global
 # CHECK-NEXT:     Type:
 # CHECK-NEXT:     Other:
 # CHECK-NEXT:     Section: Undefined
 # CHECK-NEXT:   }