main: Unregister signal handler before destroying my_perl

If the signal handler runs after perl_destruct() has been called, it
will get an invalid (or NULL) my_perl when it asks for the
thread-specific interpreter struct.  This patch resets the signal
handler for any signal previously handled by PL_csighandlerp to SIG_DFL
before calling perl_destruct().

miniperlmain.c

@@ -67,7 +67,7 @@ main(int argc, char **argv, char **env)
 #endif
 {
     dVAR;
-    int exitstatus;
+    int exitstatus, i;
 #ifdef PERL_GLOBAL_STRUCT
     struct perl_vars *plvarsp = init_global_struct();
 #  ifdef PERL_GLOBAL_STRUCT_PRIVATE
@@ -116,6 +116,13 @@ main(int argc, char **argv, char **env)
     if (!exitstatus)
         perl_run(my_perl);
 
+    /* Unregister our signal handler before destroying my_perl */
+    for (i = 0; PL_sig_name[i]; i++) {
+	if (rsignal_state(PL_sig_num[i]) == (Sighandler_t) PL_csighandlerp) {
+	    rsignal(PL_sig_num[i], (Sighandler_t) SIG_DFL);
+	}
+    }
+
     exitstatus = perl_destruct(my_perl);
 
     perl_free(my_perl);