Sergey,

This patch moves the <alias_alloc.lua> test from the <misc> to the
created <opt/mem> directory, includes it in <index>, and names subtests.

Testing optimizations in <lj_opt_mem.c> requires CSE, DCE, FOLD, and FWD
optimizations enabled. Hence, the corresponding flags are used for the
<mem> directory in <index>.

Part of tarantool/tarantool#9398
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