[WebAssembly] Don't mark lazy symbols as `IsUsedInRegularObj`

This matches the ELF does.  Update the comment in ELF/Symbols.h and
duplicate it in wasm/Symbols.h

This a followup on rL355580 and rL355577.

Differential Revision: https://reviews.llvm.org/D59075

llvm-svn: 355737
diff --git a/lld/wasm/SymbolTable.cpp b/lld/wasm/SymbolTable.cpp
index 9315e72..1e7357d 100644
--- a/lld/wasm/SymbolTable.cpp
+++ b/lld/wasm/SymbolTable.cpp
@@ -191,7 +191,7 @@
   LLVM_DEBUG(dbgs() << "addSyntheticFunction: " << Name << "\n");
   assert(!find(Name));
   SyntheticFunctions.emplace_back(Function);
-  return replaceSymbol<DefinedFunction>(insert(Name, nullptr).first, Name,
+  return replaceSymbol<DefinedFunction>(insertName(Name).first, Name,
                                         Flags, nullptr, Function);
 }
 
@@ -199,7 +199,7 @@
                                                  uint32_t Flags) {
   LLVM_DEBUG(dbgs() << "addSyntheticDataSymbol: " << Name << "\n");
   assert(!find(Name));
-  return replaceSymbol<DefinedData>(insert(Name, nullptr).first, Name, Flags);
+  return replaceSymbol<DefinedData>(insertName(Name).first, Name, Flags);
 }
 
 DefinedGlobal *SymbolTable::addSyntheticGlobal(StringRef Name, uint32_t Flags,
@@ -208,7 +208,7 @@
                     << "\n");
   assert(!find(Name));
   SyntheticGlobals.emplace_back(Global);
-  return replaceSymbol<DefinedGlobal>(insert(Name, nullptr).first, Name, Flags,
+  return replaceSymbol<DefinedGlobal>(insertName(Name).first, Name, Flags,
                                       nullptr, Global);
 }
 
@@ -442,7 +442,7 @@
 
   Symbol *S;
   bool WasInserted;
-  std::tie(S, WasInserted) = insert(Name, nullptr);
+  std::tie(S, WasInserted) = insertName(Name);
 
   if (WasInserted) {
     replaceSymbol<LazySymbol>(S, Name, 0, File, *Sym);