erts: Fix fragmented send to finish before exiting

If a process is suspended doing a fragmented send and then
receives an exit signal it was terminated before it could
finish sending the message leading to a memory leak on the
receiving side.

This change fixes that so that the message is allowed to
finish being sent before the process exits.

Closes erlang#5876

erts/emulator/beam/bif.c

@@ -54,7 +54,7 @@ static Export* flush_monitor_messages_trap = NULL;
 static Export* set_cpu_topology_trap = NULL;
 static Export* await_port_send_result_trap = NULL;
 Export* erts_format_cpu_topology_trap = NULL;
-static Export dsend_continue_trap_export;
+Export dsend_continue_trap_export;
 Export *erts_convert_time_unit_trap = NULL;
 
 static Export *await_msacc_mod_trap = NULL;

erts/emulator/beam/erl_process.c

@@ -13684,6 +13684,7 @@ enum continue_exit_phase {
     ERTS_CONTINUE_EXIT_CLEAN_SYS_TASKS,
     ERTS_CONTINUE_EXIT_FREE,
     ERTS_CONTINUE_EXIT_CLEAN_SYS_TASKS_AFTER,
+    ERTS_CONTINUE_EXIT_DIST_SEND,
     ERTS_CONTINUE_EXIT_LINKS,
     ERTS_CONTINUE_EXIT_MONITORS,
     ERTS_CONTINUE_EXIT_LT_MONITORS,
@@ -13706,6 +13707,8 @@ struct continue_exit_state {
     Uint32 block_rla_ref;
 };
 
+extern Export dsend_continue_trap_export;
+
 void
 erts_continue_exit_process(Process *p)
 {
@@ -13897,6 +13900,9 @@ erts_continue_exit_process(Process *p)
         /* notify free */
         erts_atomic32_read_bor_relb(&p->state, ERTS_PSFLG_FREE);
 
+        /* clear suspend count */
+        p->rcount = 0;
+
         trap_state->dep = ((p->flags & F_DISTRIBUTION)
                       ? ERTS_PROC_SET_DIST_ENTRY(p, NULL)
                       : NULL);
@@ -13945,15 +13951,24 @@ erts_continue_exit_process(Process *p)
         trap_state->pectxt.dist_state = NIL;
         trap_state->pectxt.yield = 0;
 
+        if (p->current == &dsend_continue_trap_export.info.mfa) {
+            trap_state->pectxt.dist_state = p->arg_reg[0];
+        }
+
         erts_proc_lock(p, ERTS_PROC_LOCK_MSGQ);
 
         erts_proc_sig_fetch(p);
 
         erts_proc_unlock(p, ERTS_PROC_LOCK_MSGQ);
 
         trap_state->yield_state = NULL;
-        trap_state->phase = ERTS_CONTINUE_EXIT_LINKS;
+        trap_state->phase = ERTS_CONTINUE_EXIT_DIST_SEND;
         if (reds <= 0) goto yield;
+    case ERTS_CONTINUE_EXIT_DIST_SEND:
+        if (is_not_nil(trap_state->pectxt.dist_state)) {
+            goto continue_dist_send;
+        }
+        trap_state->phase = ERTS_CONTINUE_EXIT_LINKS;
     case ERTS_CONTINUE_EXIT_LINKS:
 
         reds = erts_link_tree_foreach_delete_yielding(