fenv.h missing in hurd cross compiling

hi

i try to cross compiling hurd from scratch with :
http://fondriest.frederic.free.fr/hurd/GNU_HURD%20from%20scratch.html

i use this version of tools

binutils 2.25
gcc 4.8.2

i get hurd here : http://savannah.gnu.org/git/?group=hurd

additional tools are :

bash-4.3
coreutils-8.23.tar

i install on my ubuntu 14.04 LTS:
g++

makeinfo
and ncurses

when in try to compile gcc (cross-gcc (#1))

i have a fenv.h missing :

../../../gcc-4.8.2/libgcc/config/libbid/bid_decimal_globals.c:47:18: 
fatal error: fenv.h: No such file or directory
  #include <fenv.h>

can you help me ?
regard,
major_ghz

p.s. if you need more information ask me...