Return back the zero parameter of aggregate initialization in OutputSectionFactory::lookup().

That was removed in r266304, but leads to warnings by Clang.
Thanks to Rafael EspĂ­ndola for pointing on that.

Though I think change was legal from point of C++.

llvm-svn: 266306
diff --git a/lld/ELF/Writer.cpp b/lld/ELF/Writer.cpp
index c1c97d9..5822106 100644
--- a/lld/ELF/Writer.cpp
+++ b/lld/ELF/Writer.cpp
@@ -994,7 +994,7 @@
 
   OutputSectionBase<ELFT> *lookup(StringRef Name, uint32_t Type,
                                   uintX_t Flags) {
-    return Map.lookup({Name, Type, Flags});
+    return Map.lookup({Name, Type, Flags, 0});
   }
 
 private: