Revert "ScheduleDAGInstrs: Rework schedule graph builder."

This works mostly fine but breaks some stage 1 builders when compiling
compiler-rt on i386. Revert for further investigation as I can't see an
obvious cause/fix.

This reverts commit r254577.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@254586 91177308-0d34-0410-b5e6-96231b3b80d8
16 files changed