flex: Patch Makefile.in instead of Makefile.am

This avoids the following error when building under ubuntu 18.04
which has a never version of automake:

configure.ac:31: error: version mismatch.  This is Automake 1.15.1,
configure.ac:31: but the definition used by this AM_INIT_AUTOMAKE
configure.ac:31: comes from Automake 1.15.  You should recreate
configure.ac:31: aclocal.m4 with aclocal and run automake again.

packages/flex/Makefile.am.patch

@@ -1,11 +0,0 @@
-diff -u -r ../flex-2.6.0/Makefile.am ./Makefile.am
---- ../flex-2.6.0/Makefile.am	2015-11-10 17:55:38.000000000 -0500
-+++ ./Makefile.am	2015-12-27 06:36:29.059725071 -0500
-@@ -53,7 +53,6 @@
- 	doc \
- 	examples \
- 	po \
--	tests \
- 	tools
- 
- # Create the ChangeLog, but only if we're inside a git working directory

packages/flex/Makefile.in.patch

@@ -0,0 +1,11 @@
+diff -u -r ../flex-2.6.4/Makefile.in ./Makefile.in
+--- ../flex-2.6.4/Makefile.in	2017-05-06 16:49:09.000000000 +0200
++++ ./Makefile.in	2018-04-29 23:46:48.128733975 +0200
+@@ -453,7 +453,6 @@
+ 	doc \
+ 	examples \
+ 	po \
+-	tests \
+ 	tools
+ 
+ all: all-recursive