[WebAssembly] Initial support for LTO

Differential Revision: https://reviews.llvm.org/D47162

llvm-svn: 333570
diff --git a/lld/wasm/Writer.cpp b/lld/wasm/Writer.cpp
index 8e05a4d..ee6056a 100644
--- a/lld/wasm/Writer.cpp
+++ b/lld/wasm/Writer.cpp
@@ -715,6 +715,8 @@
       continue;
     if (!Sym->isLive())
       continue;
+    if (!Sym->IsUsedInRegularObj)
+      continue;
 
     LLVM_DEBUG(dbgs() << "import: " << Sym->getName() << "\n");
     ImportedSymbols.emplace_back(Sym);