$NetBSD: patch-src_Makefile.in,v 1.2 2019/07/07 18:02:44 schwarz Exp $

Let to exactly point to own diff program.
Fixes PR 39941.

--- src/Makefile.in.orig	2019-01-01 02:37:29.000000000 +0100
+++ src/Makefile.in	2019-07-07 00:38:35.000000000 +0200
@@ -1325,7 +1325,7 @@
   system.h
 
 MOSTLYCLEANFILES = paths.h paths.ht
-gdiff = `echo diff|sed '$(transform)'`
+gdiff = "%DEFAULT_DIFF_PROGRAM%"
 BUILT_SOURCES = paths.h version.c version.h
 noinst_LIBRARIES = libver.a
 nodist_libver_a_SOURCES = version.c version.h