gdbserver: remove unused variable

When building with clang 15, I got this error:

  CXX    server.o
server.cc:2985:10: error: variable 'new_argc' set but not used [-Werror,-Wunused-but-set-variable]
  int i, new_argc;
             ^
Remove the unused variable to eliminate the error.

Tested by rebuilding on x86_64-linux with clang 15.

gdbserver/server.cc

@@ -2982,14 +2982,10 @@ handle_v_run (char *own_buf)
   char *p, *next_p;
   std::vector<char *> new_argv;
   char *new_program_name = NULL;
-  int i, new_argc;
+  int i;
 
-  new_argc = 0;
   for (p = own_buf + strlen ("vRun;"); p && *p; p = strchr (p, ';'))
-    {
-      p++;
-      new_argc++;
-    }
+    p++;
 
   for (i = 0, p = own_buf + strlen ("vRun;"); *p; p = next_p, ++i)
     {