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".

src/os_win32.c

@@ -4388,7 +4388,8 @@ sub_process_writer(LPVOID param)
 		    && (lnum != curbuf->b_ml.ml_line_count
 			|| curbuf->b_p_eol)))
 	    {
-		WriteFile(g_hChildStd_IN_Wr, "\n", 1, (LPDWORD)&ignored, NULL);
+		WriteFile(g_hChildStd_IN_Wr, "\n", 1,
+						  (LPDWORD)&vim_ignored, NULL);
 	    }
 
 	    ++lnum;