remove the older dwarf5 and atomics patch

Author: zhuowei

lib/IRGen/IRGen.cpp

@@ -162,11 +162,6 @@ swift::getIRTargetOptions(const IRGenOptions &Opts, ASTContext &Ctx) {
   // Explicitly request debugger tuning for LLDB which is the default
   // on Darwin platforms but not on others.
   TargetOpts.DebuggerTuning = llvm::DebuggerKind::LLDB;
-
-  // WebAssembly HACK: disable atomics
-  if (Ctx->LangOpts.Target.isOSBinFormatWasm()) {
-    TargetOpts.ThreadModel = llvm::ThreadModel::Single;
-  }
   TargetOpts.FunctionSections = Opts.FunctionSections;
 
   auto *Clang = static_cast<ClangImporter *>(Ctx.getClangModuleLoader());