Include: Fix command line parser hang when threaded.

include/verilated.cpp

@@ -1678,7 +1678,7 @@ void Verilated::flushCall() VL_MT_SAFE {
 }
 
 void Verilated::commandArgs(int argc, const char** argv) VL_MT_SAFE {
-    VerilatedLockGuard lock(m_mutex);
+    VerilatedLockGuard lock(s_args.m_argMutex);
     s_args.argc = argc;
     s_args.argv = argv;
     VerilatedImp::commandArgs(argc,argv);

include/verilated.h

@@ -347,6 +347,7 @@ class Verilated {
     // no need to be save-restored (serialized) the
     // assumption is that the restore is allowed to pass different arguments
     static struct CommandArgValues {
+        VerilatedMutex m_argMutex;  ///< Mutex for s_args members, when VL_THREADED
 	int          argc;
 	const char** argv;
         CommandArgValues() : argc(0), argv(NULL) {}