component/flex: version up 2.6.4

component/flex/buildout.cfg

@@ -9,8 +9,10 @@ parts =
 [flex]
 recipe = slapos.recipe.cmmi
 shared = true
-url = http://downloads.sourceforge.net/project/flex/flex-2.6.0.tar.xz
-md5sum = 3cbbfa1554d0b75fad9f8100732454de
+url = https://github.com/westes/flex/releases/download/v2.6.4/flex-2.6.4.tar.gz
+md5sum = 2882e3179748cc9f9c23ec593d6adc8d
 environment =
   M4=${m4:location}/bin/m4
   PATH=${bison:location}/bin:${xz-utils:location}/bin:%(PATH)s
+# CFLAGS to workaround https://github.com/westes/flex/issues/442
+  CFLAGS=-g -O2 -D_GNU_SOURCE