flex: disable building po, tools

Amend the patch that disabled tests and docs to remove everything but
the src dir that builds the main flex program--the only file packaged.

Signed-off-by: Eneas U de Queiroz <cotequeiroz@gmail.com>

devel/flex/patches/100-disable-all-dirs-except-src.patch

@@ -0,0 +1,16 @@
+--- a/Makefile.am
++++ b/Makefile.am
+@@ -42,12 +42,7 @@ EXTRA_DIST = \
+ 	autogen.sh
+ 
+ SUBDIRS = \
+-	src \
+-	doc \
+-	examples \
+-	po \
+-	tests \
+-	tools
++	src
+ 
+ # Create the ChangeLog, but only if we're inside a git working directory
+