[Wasm][LTO][NPM] Use NPM for LTO with ENABLE_EXPERIMENTAL_NEW_PASS_MANAGER

[MaskRay]

On the ELF side we have switched to --no-lto-legacy-pass-manager --lto-legacy-pass-manager and dropped --[no-]lto-new-pass-manager...

The driver uses -plugin-opt={new,legacy}-pass-manager

[aeubanks]

I can do that in a follow up change, I'd like to land this separately since it's two different functionality changes.

[MaskRay]

LGTM.

lld/wasm/Driver.cpp

 #include "lld/Common/Args.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/Filesystem.h"
 #include "lld/Common/Memory.h"
 #include "lld/Common/Reproduce.h"
 #include "lld/Common/Strings.h"
 #include "lld/Common/Version.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Config/llvm-config.h"
 #include "llvm/Object/Wasm.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/Parallel.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
static void readConfigs(opt::InputArgList &args) {
   config->growableTable = args.hasArg(OPT_growable_table);
   errorHandler().fatalWarnings =
       args.hasFlag(OPT_fatal_warnings, OPT_no_fatal_warnings, false);
   config->importMemory = args.hasArg(OPT_import_memory);
   config->sharedMemory = args.hasArg(OPT_shared_memory);
   config->importTable = args.hasArg(OPT_import_table);
   config->ltoo = args::getInteger(args, OPT_lto_O, 2);
   config->ltoPartitions = args::getInteger(args, OPT_lto_partitions, 1);
-  config->ltoNewPassManager = args.hasFlag(OPT_lto_new_pass_manager,
-                                           OPT_no_lto_new_pass_manager, false);
+  config->ltoNewPassManager =
+      args.hasFlag(OPT_lto_new_pass_manager, OPT_no_lto_new_pass_manager,
+                   LLVM_ENABLE_NEW_PASS_MANAGER);
   config->ltoDebugPassManager = args.hasArg(OPT_lto_debug_pass_manager);
   config->mapFile = args.getLastArgValue(OPT_Map);
   config->optimize = args::getInteger(args, OPT_O, 0);
   config->outputFile = args.getLastArgValue(OPT_o);
   config->relocatable = args.hasArg(OPT_relocatable);
   config->gcSections =
       args.hasFlag(OPT_gc_sections, OPT_no_gc_sections, !config->relocatable);
   config->mergeDataSegments =