Add message for unknown cbmc option

regression/cbmc/bad_option/main.c

@@ -0,0 +1,3 @@
+int main() {
+  return 0;
+}

regression/cbmc/bad_option/test.desc

@@ -0,0 +1,7 @@
+CORE
+main.c
+-foo
+^EXIT=(64|1)$
+^SIGNAL=0$
+Unknown option: -foo
+--

regression/cbmc/bad_option/test_multiple.desc

@@ -0,0 +1,7 @@
+CORE
+main.c
+--trace --foo --refine-strings
+^EXIT=(64|1)$
+^SIGNAL=0$
+Unknown option: --foo
+--

src/util/cmdline.cpp

@@ -185,7 +185,10 @@ bool cmdlinet::parse(int argc, const char **argv, const char *optstring)
       }
 
       if(optnr<0)
+      {
+        unknown_arg=argv[i];
         return true;
+      }
       options[optnr].isset=true;
       if(options[optnr].hasval)
       {

src/util/cmdline.h

@@ -33,6 +33,7 @@ class cmdlinet
 
   typedef std::vector<std::string> argst;
   argst args;
+  std::string unknown_arg;
 
   cmdlinet();
   virtual ~cmdlinet();

src/util/parse_options.cpp

@@ -37,11 +37,20 @@ void parse_options_baset::usage_error()
   help();
 }
 
+/// Print an error message mentioning the option that was not recognized when
+/// parsing the command line.
+void parse_options_baset::unknown_option_msg()
+{
+  if(!cmdline.unknown_arg.empty())
+    std::cerr << "Unknown option: " << cmdline.unknown_arg << "\n";
+}
+
 int parse_options_baset::main()
 {
   if(parse_result)
   {
     usage_error();
+    unknown_option_msg();
     return EX_USAGE;
   }
 

src/util/parse_options.h

@@ -31,6 +31,7 @@ class parse_options_baset
   virtual ~parse_options_baset() { }
 
 private:
+  void unknown_option_msg();
   bool parse_result;
 };