ARM: Enable MachineScheduler and disable PostRAScheduler for swift.

This is mostly done to disable the PostRAScheduler which optimizes for
instruction latencies which isn't a good fit for out-of-order
architectures. This also allows to leave out the itinerary table in
swift in favor of the SchedModel ones.

This change leads to performance improvements/regressions by as much as
10% in some benchmarks, in fact we loose 0.4% performance over the
llvm-testsuite for reasons that appear to be unknown or out of the
compilers control. rdar://20803802 documents the investigation of
these effects.

While it is probably a good idea to perform the same switch for the
other ARM out-of-order CPUs, I limited this change to swift as I cannot
perform the benchmark verification on the other CPUs.

Differential Revision: http://reviews.llvm.org/D10513

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@242500 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCSchedule.h

@@ -206,6 +206,9 @@ struct MCSchedModel {
   /// scheduling class (itinerary class or SchedRW list).
   bool isComplete() const { return CompleteModel; }
 
+  /// Return true if machine supports out of order execution.
+  bool isOutOfOrder() const { return MicroOpBufferSize > 1; }
+
   unsigned getNumProcResourceKinds() const {
     return NumProcResourceKinds;
   }