force pystub to be linked into interrogate and interrogate_module

dtool/src/interrogate/interrogate.cxx

@@ -305,6 +305,9 @@ predefine_macro(CPPParser& parser, const string& inoption) {
 
 int
 main(int argc, char **argv) {
+  // A call to pystub() to force libpystub.so to be linked in.
+  pystub();
+
   preprocess_argv(argc, argv);
   string command_line;
   int i;

dtool/src/interrogate/interrogate_module.cxx

@@ -238,6 +238,9 @@ int main(int argc, char *argv[]) {
   extern int optind;
   int flag;
 
+  // A call to pystub() to force libpystub.so to be linked in.
+  pystub();
+
   preprocess_argv(argc, argv);
   flag = getopt_long_only(argc, argv, short_options, long_options, NULL);
   while (flag != EOF) {