To make tarantool-gc64 available in repository we need to provide
a product name in a package itself and in the repository.

To build Tarantool with gc64 enabled, the flag -DLUAJIT_ENABLE_GC64
needs to be passed to cmake flags. For this purposes GC64 env var
was added to all workflows for Debian, Ubuntu, Centos and Fedora.

This variable is processed to rename PRODUCT_NAME. If GC64 is
eanbled, PRODUCT_NAME is `tarantool-gc64`, otherwise it stays
`tarantool`, which goes to repository name and the package itself.
Thus, Tarantool with gc64 enabled can be installed by
`<packaen_manager> install -y tarantool-gc64`
in the one single repository.

NO_DOC=ci
NO_TEST=ci
NO_CHANGELOG=ci

Closes: tarantool/tarantool-qa#161