Work around empty set default parameter compilation issue.

src/IceRegAlloc.h

@@ -32,7 +32,7 @@ class LinearScan {
 
 public:
   explicit LinearScan(Cfg *Func);
-  void init(RegAllocKind Kind, CfgSet<Variable *> ExcludeVars = {});
+  void init(RegAllocKind Kind, CfgSet<Variable *> ExcludeVars);
   void scan(const SmallBitVector &RegMask, bool Randomized);
   // Returns the number of times some variable has been assigned a register but
   // later evicted because of a higher-priority allocation.  The idea is that we

src/IceTargetLowering.cpp

@@ -514,8 +514,9 @@ void TargetLowering::regAlloc(RegAllocKind Kind) {
     RegExclude |= RegSet_FramePointer;
   SmallBitVector RegMask = getRegisterSet(RegInclude, RegExclude);
   bool Repeat = (Kind == RAK_Global && getFlags().getRepeatRegAlloc());
+  CfgSet<Variable *> EmptySet;
   do {
-    LinearScan.init(Kind);
+    LinearScan.init(Kind, EmptySet);
     LinearScan.scan(RegMask, getFlags().getRandomizeRegisterAllocation());
     if (!LinearScan.hasEvictions())
       Repeat = false;