[lld][WebAssembly] Fix __start/__stop symbols when combining input segments

We should be generating one __start/__stop pair per output segment
not per input segment.  The test wasn't catching this because it was
only linking a single object file.

Fixes PR41565

Differential Revision: https://reviews.llvm.org/D64148

llvm-svn: 365308
diff --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
index 74d3132..aab3724 100644
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -228,6 +228,7 @@
   LLVM_DEBUG(dbgs() << "addOptionalDataSymbol: " << Name << "\n");
   auto *rtn = replaceSymbol<DefinedData>(S, Name, Flags);
   rtn->setVirtualAddress(Value);
+  rtn->Referenced = true;
   return rtn;
 }