Remove the '-disable-scheduling' flag and replace it with the 'source' option of

Remove the '-disable-scheduling' flag and replace it with the 'source' option of
the '-pre-RA-sched' flag. It actually makes more sense to do it this way. Also,
keep track of the SDNode ordering by default. Eventually, we would like to make
this ordering a way to break a "tie" in the scheduler. However, doing that now
breaks the "CodeGen/X86/abi-isel.ll" test for 32-bit Linux.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@94308 91177308-0d34-0410-b5e6-96231b3b80d8