Patch found on https://bugs.archlinux.org/task/3460?getfile=430
--
this lets bc use readline-4.2, borrowed from redhat apparently. :)

--- bc-1.06/bc/scan.l.sux	Fri May 11 14:27:20 2001
+++ bc-1.06/bc/scan.l	Fri May 11 14:27:32 2001
@@ -143,7 +143,6 @@
 
 /* Definitions for readline access. */
 extern FILE *rl_instream;
-_PROTOTYPE(char *readline, (char *));
 
 /* rl_input puts upto MAX characters into BUF with the number put in
    BUF placed in *RESULT.  If the yy input file is the same as
--- ./configure.orig	2013-06-22 22:32:34.270270254 +0200
+++ ./configure	2013-06-22 22:32:41.257270269 +0200
@@ -2245,7 +2245,7 @@
 
 
 if test "$LEX" = "flex" ; then
- LEX="flex -I8"
+ LEX="flex -I"
 else
  if test "$bcrl" = "y" ; then
   echo "configure: warning: readline works only with flex." 1>&2