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

@@ -923,7 +923,8 @@ 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

@@ -522,7 +522,8 @@ 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);