Bug#682689: buildcross fails to build gcc-4.7

[sacrificial-spam-address@horizon.com]

Package: buildcross
Version: 0.0.12

This is due to line 1095 of /usr/lib/buildcross/functions, which
defines the em_cross function:

case ${1} in
	# (other cases omitted)
        gcc-3.[3-4]|gcc-4.[0-6])
                GCCVER=${1#gcc-}
                myecho INFO "I: Building GCC ${GCCVER}"
                checkinstalled gcc-${GCCVER}
                install-gcc-build-deps ${GCCVER}
                build-gcc ${GCCVER} > $LOGPATH/$HOSTARCH-$DEBARCH-$PKG.log 2>&1
                #install-gcc ${GCCVER}
                ;;

There is no obvious reason why this case couldn't be extended, and in
fact I have successfully built a gcc-4.7 package by doing so.

Another useful addition to this function would be a catch-all error
case, rather than failing silently.