RFR(XS): 8234350: assert(mode == ControlAroundStripMined && (use == sfpt || !use->is_reachable_from_root())) failed: missed a node

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8234350/webrev.00/

This is the same issue and fix as 8230061 (dead nodes in the outer strip
mined loop should be ignored in verification code when cloning the loop
body). The only difference is that the assert is relaxed so it applies
to all forms of cloning where the outer strip mined loop is involved.

Roland.