gentoo: add prefix-dir 'compression'
gentoo: add prefix-dir 'compression'

Former-commit-id: d0c0ab4e875346fe4e2e40dd7178fdc9ad9ee0f2
Former-commit-id: 766dae4002bd244b09bcfc3be3c4dd57d8ac7f7c [formerly 9f3f242e58fe401dad399d0fee37a0030273942a] [formerly b6049ae539c8c247a30abe80a39f3d95202bbc59 [formerly 4e4940c6c7aa08eea7e58cf730b45b1be466f4cd]]
Former-commit-id: 21ca610ef6bc61769e2557c85a3772ae01e2aad2 [formerly bb714217edf694175585a7db7cdf01b36d4e49bd]
Former-commit-id: 6446f3b00e6bcb7338c580eec25abce3289fa7ef
PolyJIT/benchbuild,PolyJIT/benchbuild,PolyJIT/benchbuild,PolyJIT/benchbuild