lang/gcc6-aux: Upgrade version 20161221 => 20170202 (gcc 6.3 snapshot)

The gcc6-aux compiler is being prepared to support aarch63. The last
release, 6.3.0, is missing backported support for aarch64 in general
and aarch64-*-freebsd* in particularly. Do a rare update the latest
snapshot in order to capture aarch64 support.