Fix build with GCC 11.2

--- src/cmdline.cc

+++ src/cmdline.cc

@@ -21,7 +21,7 @@

 // constructor

-Cmdline::Cmdline(int argc, char *argv[]) throw (string)

+Cmdline::Cmdline(int argc, char *argv[])

 {

   extern char *optarg;

   extern int optind;

--- src/cmdline.h

+++ src/cmdline.h

@@ -37,7 +37,7 @@ private:

 public:

   /* constructor and destructor */

-  Cmdline(int, char **) throw(string);

+  Cmdline(int, char **);

   ~Cmdline(){}

   /* usage function */