Allow RPMS to be built on ppc64 and aarch64 by making luajit optional

Allow RPMS to be built on ppc64 and aarch64 by making luajit optional

Not all architectures have luajit supported.  The bcc configure and
build were already was set up to make the luajit dependent parts
optional.  The bcc.spec now makes the luajit dependent parts optional
too allowing Fedora 25 builds on ppc64, ppc64le, and aarch64.  This
change has been tested and allows the resulting srpm to build on the
Fedora koji build system for the newly added architectures.

Signed-off-by: William Cohen <wcohen@redhat.com>