please try this.  it works for me.
-mike

2011-10-19  Mike Frysinger  <vapier@gentoo.org>

	* acinclude.m4 (SIM_AC_OPTION_HARDWARE): Check libm for log2 when
	cfi is in the hardware list.

diff --git a/sim/common/acinclude.m4 b/sim/common/acinclude.m4
index 70feca4..35ad690 100644
--- a/sim/common/acinclude.m4
+++ b/sim/common/acinclude.m4
@@ -639,6 +639,10 @@ fi
 if test x"$silent" != x"yes"; then
   echo "Setting hardware to $sim_hw_cflags, $sim_hw, $sim_hw_objs"
 fi])dnl
+dnl Some devices require extra libraries.
+case " $hardware " in
+  *" cfi "*) AC_CHECK_LIB(m, log2);;
+esac
 ])
 AC_SUBST(sim_hw_cflags)
 AC_SUBST(sim_hw_objs)