IT instructions are considered to be scheduling hazards, but are scheduled

IT instructions are considered to be scheduling hazards, but are scheduled
with the following instructions. This is done via trickery by considering the
instruction preceding the IT to be the hazard. Care must be taken to ensure
it's the first non-debug instruction, or the presence of debug info will
affect codegen.

Part of the continuing work for rdar://7797940, making ARM code-gen unaffected
by the presence of debug information.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@106871 91177308-0d34-0410-b5e6-96231b3b80d8