[Clfs-support] can't configure GRUB-2.00: flex is not found

[hot at posteo.net]

Hi, I got a problem with configuring grub (configure: error: flex is not found).

Book-Version: 3.0.0-SYSVINIT
The host distribution: Debian Wheezy 7.8
The architecture of the host and target: Both x86_64
${CLFS_HOST}: x86_64-cross-linux-gnu
${CLFS_TARGET}: x86_64-unknown-linux-gnu
${BUILD64}: -m64
The package or section in which the problem was encountered: 7.10. (Book-Chapter), GRUB-2.00
Note whether you have deviated from the book at all: No, I haven't.
The exact error message or symptom received:

While configuring GRUB-2.00 I get the following error:

clfs at testmachine:/mnt/clfs/sources/grub-2.00$ ./configure --prefix=/tools \
>     --build=${CLFS_HOST} --host=${CLFS_TARGET} \
>     --disable-werror --enable-grub-mkfont=no --with-bootdir=tools/boot
checking build system type... x86_64-cross-linux-gnu
checking host system type... x86_64-unknown-linux-gnu
checking target system type... x86_64-unknown-linux-gnu
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for x86_64-unknown-linux-gnu-strip... x86_64-unknown-linux-gnu-strip
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
checking for cmp... cmp
checking for bison... bison
checking for x86_64-unknown-linux-gnu-ranlib... x86_64-unknown-linux-gnu-ranlib
checking for gawk... (cached) gawk
checking for style of include used by make... GNU
checking for x86_64-unknown-linux-gnu-gcc... x86_64-unknown-linux-gnu-gcc -m64
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... yes
checking for suffix of object files... o
checking whether we are using the GNU C compiler... yes
checking whether x86_64-unknown-linux-gnu-gcc -m64 accepts -g... yes
checking for x86_64-unknown-linux-gnu-gcc -m64 option to accept ISO C89... none needed
checking dependency style of x86_64-unknown-linux-gnu-gcc -m64... gcc3
checking for flex... no
checking for lex... no
checking for bison... (cached) bison
checking whether make sets $(MAKE)... (cached) yes
checking whether ln -s works... yes
configure: error: flex is not found

My bash-history:
  516  tar -xf linux-3.14.tar.xz 
  517  cd linux-3.14
  518  xzcat ../patch-3.14.21.xz | patch -Np1 -i -
  519  make mrproper
  520  make ARCH=x86_64 CROSS_COMPILE=${CLFS_TARGET}- menuconfig
  521  make ARCH=x86_64 CROSS_COMPILE=${CLFS_TARGET}- menuconfig
  522  make ARCH=x86_64 CROSS_COMPILE=${CLFS_TARGET}- menuconfig
  523  make ARCH=x86_64 CROSS_COMPILE=${CLFS_TARGET}- menuconfig
  524  make ARCH=x86_64 CROSS_COMPILE=${CLFS_TARGET}- menuconfig
  525  cp .config ../../
  526  make ARCH=x86_64 CROSS_COMPILE=${CLFS_TARGET}-
  527  mkdir -pv /tools/boot
  528  cp -v arch/x86_64/boot/bzImage /tools/boot/vmlinuz-clfs-3.14.21
  529  cp -v System.map /tools/boot/System.map-3.14.21
  530  cp -v .config /tools/boot/config-3.14.21
  531  cd ../
  532  yes | rm -r linux-3.14
  533  ls -la linux-3.14.tar.xz 
  534  du -sh linux-3.14.tar.xz 
  535  tar -xf grub-2.00.tar.xz 
  536  cd grub-2.00
  537  cp -v grub-core/gnulib/stdio.in.h{,.orig}
  538  sed -e '/gets is a/d' grub-core/gnulib/stdio.in.h.orig > grub-core/gnulib/stdio.in.h
  539* ./configure --prefix=/tools     --build=${CLFS_HOST} --host=${CLFS_TARGET}     --disable-werror --enable-grub-mkfont=no --with-bootdir=tools/boot

Should I install flex from here http://sourceforge.net/projects/flex/files/? I'm asking because I'm afraid of deviating from the book.

What should I do?

Regards,
Toni