added description for ebuild env var
added description for ebuild env var


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Former-commit-id: ff5cf648f38087dc735ec8e84655ce0d1a08872d [formerly 5e39ae1d5abb103fc70810a1ef3e10e52f27fee0]
Former-commit-id: c93f7749d596aa9141e7aba33670f8e2b19ef6bb
PolyJIT/benchbuild,PolyJIT/benchbuild,PolyJIT/benchbuild,PolyJIT/benchbuild