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/term.c b/src/term.c
index b2e2b03..a92f04e 100644
--- a/src/term.c
+++ b/src/term.c
@@ -7013,7 +7013,7 @@
 		size_t	len;
 		int	pos;
 
-		ignoredp = fgets(line, LINE_LEN, fd);
+		vim_ignoredp = fgets(line, LINE_LEN, fd);
 		len = strlen(line);
 
 		if (len <= 1 || line[len - 1] != '\n')