[LLD] [COFF] Fix -Wmissing-field-initializers warnings. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@374873 91177308-0d34-0410-b5e6-96231b3b80d8

COFF/SymbolTable.cpp

@@ -157,7 +157,7 @@ std::vector<std::string> getSymbolLocations(ObjFile *file, uint32_t symIndex) {
       if (fileLine)
         locations.push_back({sym, *fileLine});
       else if (sym)
-        locations.push_back({sym});
+        locations.push_back({sym, {"", 0}});
     }
   }