Bug with 4-cycle loaduse

[jerryz123]

There's a bug with 4-cycle load-use. Here are two runs in which it appeared. The first is a dual-core config booting buildroot Linux. The second is a single-core config booting Fedora.

id: 1190, module: IssueSlot_4, path: FireBoomNoNIC.tile_1.core.issue_units_0.slots_3]
Assertion failed
    at issue_slot.scala:214 assert (!slot_p1_poisoned)
    at cycle: 2142042185

[id: 601, module: IssueSlot_4, path: FireBoomNoNIC.tile.core.issue_units_0.slots_2]
Assertion failed
    at issue_slot.scala:216 assert (!slot_p1_poisoned)
 at cycle: 195769823414