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 */