Avoid parsing -mllvm* command-line options if there aren't any

LLD somehow uses a different global LLVM command-line parser than LDC,
one with no registered options, so parsing is guaranteed to fail, even
if there are no args.
[It's only needed for LTO codegen options anyway.]

Author: kinke

COFF/Driver.cpp

@@ -1086,7 +1086,8 @@ void LinkerDriver::link(ArrayRef<const char *> argsArr) {
   v.push_back("lld-link (LLVM option parsing)");
   for (auto *arg : args.filtered(OPT_mllvm))
     v.push_back(arg->getValue());
-  cl::ParseCommandLineOptions(v.size(), v.data());
+  if (v.size() > 1)
+    cl::ParseCommandLineOptions(v.size(), v.data());
 
   // Handle /errorlimit early, because error() depends on it.
   if (auto *arg = args.getLastArg(OPT_errorlimit)) {

wasm/Driver.cpp

@@ -687,7 +687,8 @@ void LinkerDriver::link(ArrayRef<const char *> argsArr) {
   v.push_back("wasm-ld (LLVM option parsing)");
   for (auto *arg : args.filtered(OPT_mllvm))
     v.push_back(arg->getValue());
-  cl::ParseCommandLineOptions(v.size(), v.data());
+  if (v.size() > 1)
+    cl::ParseCommandLineOptions(v.size(), v.data());
 
   errorHandler().errorLimit = args::getInteger(args, OPT_error_limit, 20);