patch 8.1.0377: xdiff doesn't use the Vim memory allocation functions

Problem:    Xdiff doesn't use the Vim memory allocation functions.
Solution:   Change the xdl_ defines.  Check for out-of-memory.  Rename
            "ignored" to "vim_ignored".
diff --git a/src/ui.c b/src/ui.c
index 8e3f0de..1765620 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -403,7 +403,7 @@
     void
 ui_breakcheck_force(int force)
 {
-    int save_us = updating_screen;
+    int save_updating_screen = updating_screen;
 
     /* We do not want gui_resize_shell() to redraw the screen here. */
     ++updating_screen;
@@ -415,8 +415,8 @@
 #endif
 	mch_breakcheck(force);
 
-    if (save_us)
-	updating_screen = save_us;
+    if (save_updating_screen)
+	updating_screen = TRUE;
     else
 	reset_updating_screen(FALSE);
 }
@@ -1885,7 +1885,7 @@
 #ifdef HAVE_DUP
 	    /* Use stderr for stdin, also works for shell commands. */
 	    close(0);
-	    ignored = dup(2);
+	    vim_ignored = dup(2);
 #else
 	    read_cmd_fd = 2;	/* read from stderr instead of stdin */
 #endif