flex: disable examples, po and tests

Works around a build failure with make 4.3.

packages/devel/flex/patches/flex-002-nocrap.patch

@@ -0,0 +1,13 @@
+--- a/Makefile.am	2020-01-08 12:57:40.940081434 +0100
++++ b/Makefile.am	2020-01-08 12:57:59.603818146 +0100
+@@ -50,10 +50,6 @@
+ SUBDIRS = \
+ 	lib \
+ 	src \
+-	doc \
+-	examples \
+-	po \
+-	tests \
+ 	tools
+ 
+ # Create the ChangeLog, but only if we're inside a git working directory

packages/devel/flex/patches/flex-002-nodocs.patch

@@ -1,10 +0,0 @@
---- flex-2.5.39/Makefile.am.orig	2017-01-26 21:20:07.947836925 +0900
-+++ flex-2.5.39/Makefile.am	2017-01-26 21:20:20.332836652 +0900
-@@ -117,7 +117,6 @@
- SUBDIRS = \
- 	lib \
- 	src \
--	doc \
- 	examples \
- 	po \
- 	tests