cups-filters: needs at least gcc 4.8 for C++11 features

cups-filters: needs at least gcc 4.8 for C++11 features

With gcc 4.7, it fails to build with:

checking whether /home/buildroot/build/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-g++ supports C++11 features by default... no
checking whether /home/buildroot/build/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-g++ supports C++11 features with -std=c++11... no
checking whether /home/buildroot/build/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-g++ supports C++11 features with +std=c++11... no
checking whether /home/buildroot/build/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-g++ supports C++11 features with -h std=c++11... no
checking whether /home/buildroot/build/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-g++ supports C++11 features with -std=c++0x... no
checking whether /home/buildroot/build/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-g++ supports C++11 features with +std=c++0x... no
checking whether /home/buildroot/build/instance-0/output/host/bin/powerpc-ctng_e500v2-linux-gnuspe-g++ supports C++11 features with -h std=c++0x... no
configure: error: *** A compiler with support for C++11 language features is required.

Fixes:

  http://autobuild.buildroot.net/results/788c1a4bbc8ec90b5cdd94c107c784df21869f6c/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>