fcgiwrap: disable -Werror in CFLAGS

fcgiwrap: disable -Werror in CFLAGS

fcgiwrap's configure script appends -Werror to AM_CFLAGS, then use it
to build the package.  This is an issue when Buildroot supports a new
compiler version and this version makes some warnings appear.
Luckily, one can provide CFLAGS=-Wno-error to the configure script so
it appends -Wno-error to AM_CFLAGS.

Fixes:

  http://autobuild.buildroot.net/results/8e04bf5a85ecd7f120bc9dedeedc891def6c46c1/

Signed-off-by: Thomas Claveirole <thomas.claveirole@green-communications.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>