mk: use $CC to detect toolchain version
mk: use $CC to detect toolchain version

Using gcc is wrong, we should use the cross gcc to detect the
version of gcc.

Signed-off-by: Samuel Gauthier <6d23d650162ce2a9a3e654b5ebd92694dbd28c4a@6wind.com>
Acked-by: Thomas Monjalon <ee2fa8b2681c737f775687e475dcbf2028a412f1@6wind.com>

msune/dpdk,mixja/dpdk,venkynv/dpdk-mirror,venkynv/dpdk-mirror,venkynv/dpdk-mirror,tsphillips/dpdk-fork,msune/dpdk,john-mcnamara-intel/dpdk,mixja/dpdk,msune/dpdk,john-mcnamara-intel/dpdk,mixja/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,msune/dpdk,john-mcnamara-intel/dpdk,mixja/dpdk,tsphillips/dpdk-fork