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/evalfunc.c b/src/evalfunc.c
index 19e2657..ff54589 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -14016,7 +14016,7 @@
 	else if (do_fsync)
 	    /* Ignore the error, the user wouldn't know what to do about it.
 	     * May happen for a device. */
-	    ignored = fsync(fileno(fd));
+	    vim_ignored = fsync(fileno(fd));
 #endif
 	fclose(fd);
     }