Fix race condition in jump table list creation

src/IceSwitchLowering.h

 //===- subzero/src/IceSwitchLowering.h - Switch lowering --------*- C++ -*-===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 63 matching lines @@
   bool tryAppend(const CaseCluster &New);
 };
 
 /// Store the jump table data so that it can be emitted later in the correct ELF
 /// section once the offsets from the start of the function are known.
 class JumpTableData {
   JumpTableData() = delete;
   JumpTableData &operator=(const JumpTableData &) = delete;
 
 public:
-  JumpTableData(IceString FuncName, SizeT Id, SizeT NumTargets)
-      : FuncName(FuncName), Id(Id) {
-    TargetOffsets.reserve(NumTargets);
-  }
+  using TargetList = std::vector<intptr_t>;
+
+  JumpTableData(const IceString &FuncName, SizeT Id,
+                const TargetList &TargetOffsets)
+      : FuncName(FuncName), Id(Id), TargetOffsets(TargetOffsets) {}
   JumpTableData(const JumpTableData &) = default;
   JumpTableData(JumpTableData &&) = default;
   JumpTableData &operator=(JumpTableData &&) = default;
 
-  void pushTarget(intptr_t Offset) { TargetOffsets.emplace_back(Offset); }
-
   const IceString &getFunctionName() const { return FuncName; }
   SizeT getId() const { return Id; }
-  const std::vector<intptr_t> &getTargetOffsets() const {
-    return TargetOffsets;
-  }
+  const TargetList &getTargetOffsets() const { return TargetOffsets; }
 
 private:
   IceString FuncName;
   SizeT Id;
-  std::vector<intptr_t> TargetOffsets;
+  TargetList TargetOffsets;
 };
 
 using JumpTableDataList = std::vector<JumpTableData>;
 
 } // end of namespace Ice
 
 #endif //  SUBZERO_SRC_ICESWITCHLOWERING_H