patch 8.2.4010: error messages are spread out

Problem:    Error messages are spread out.
Solution:   Move more error messages to errors.h.
diff --git a/src/gui.c b/src/gui.c
index 2e2097d..4aae106 100644
--- a/src/gui.c
+++ b/src/gui.c
@@ -241,7 +241,7 @@
     pid = fork();
     if (pid < 0)	    // Fork error
     {
-	emsg(_("E851: Failed to create a new process for the GUI"));
+	emsg(_(e_failed_to_create_new_process_for_GUI));
 	return;
     }
     else if (pid > 0)	    // Parent
@@ -265,7 +265,7 @@
 # else
 		waitpid(pid, &exit_status, 0);
 # endif
-		emsg(_("E852: The child process failed to start the GUI"));
+		emsg(_(e_the_child_process_failed_to_start_GUI));
 		return;
 	    }
 	    else if (status == GUI_CHILD_IO_ERROR)