MC: Remove the copy of MCSchedModel in MCSubtargetInfo

`MCSchedModel` is large.  Make `MCSchedModel::GetDefaultSchedModel()`
return by-reference instead of by-value, so we can store a pointer in
`MCSubtargetInfo::CPUSchedModel` instead of a copy.

Note: since `MCSchedModel` is POD, this doesn't create a static
constructor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241947 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCSchedule.h

@@ -224,25 +224,9 @@ struct MCSchedModel {
     return &SchedClassTable[SchedClassIdx];
   }
 
-  // /\brief Returns a default initialized model. Used for unknown processors.
-  static MCSchedModel GetDefaultSchedModel() {
-    MCSchedModel Ret = { DefaultIssueWidth,
-                         DefaultMicroOpBufferSize,
-                         DefaultLoopMicroOpBufferSize,
-                         DefaultLoadLatency,
-                         DefaultHighLatency,
-                         DefaultMispredictPenalty,
-                         false,
-                         true,
-                         0,
-                         nullptr,
-                         nullptr,
-                         0,
-                         0,
-                         nullptr
-                       };
-    return Ret;
-  }
+  /// Returns the default initialized model.
+  static const MCSchedModel &GetDefaultSchedModel() { return Default; }
+  static const MCSchedModel Default;
 };
 
 } // End llvm namespace