Revert "auto merge of #8328 : alexcrichton/rust/llvm-head, r=brson"

This reverts commit a8c3fe45c6138cd1f4d143fdb0e843ee2d4759b2, reversing
changes made to 67c954e365970e4c2cd06f0c50724656d7010f45.
auto merge of #8714 : brson/rust/llvm-revert, r=brson

This reverts commit a8c3fe45c6138cd1f4d143fdb0e843ee2d4759b2, reversing
changes made to 67c954e365970e4c2cd06f0c50724656d7010f45.

Reverting until #8665 is figured out.