Stefan Fiedler:

package/base/flex/flex.conf

@@ -20,6 +20,9 @@
 # 
 # --- ROCK-COPYRIGHT-NOTE-END ---
 
+# Avoids using the wrong asm/ headers.
+var_append confopt ' ' '--includedir=$includedir'
+var_append makeinstopt ' ' 'includedir=${includedir#$root}'
 
 pkg_flex_postmake() {
 	echo -e '#!/bin/sh\nexec flex -l "$@"' > $instroot/usr/bin/lex