Allow targets more controls on what nodes are scheduled by reg pressure, what for latency in hybrid mode.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104293 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Target/TargetMachine.h

@@ -72,6 +72,7 @@ namespace CodeGenOpt {
 
 namespace Sched {
   enum Preference {
+    None,             // No preference
     Latency,          // Scheduling for shortest total latency.
     RegPressure,      // Scheduling for lowest register pressure.
     Hybrid            // Scheduling for both latency and register pressure.