Make ARM RegNames[] static like X86 (no ARM syms in X86-only build).

src/IceTargetLoweringMIPS32.h

 //===- subzero/src/IceTargetLoweringMIPS32.h - MIPS32 lowering ---*- C++-*-===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 111 matching lines @@
       const llvm::SmallBitVector &ExcludeRegisters) const override;
 
   static Type stackSlotType();
 
   bool UsesFramePointer = false;
   bool NeedsStackAlignment = false;
   llvm::SmallBitVector TypeToRegisterSet[IceType_NUM];
   llvm::SmallBitVector ScratchRegs;
   llvm::SmallBitVector RegsUsed;
   VarList PhysicalRegisters[IceType_NUM];
-  static IceString RegNames[];
 
 private:
   ~TargetMIPS32() override = default;
 };
 
 class TargetDataMIPS32 final : public TargetDataLowering {
   TargetDataMIPS32() = delete;
   TargetDataMIPS32(const TargetDataMIPS32 &) = delete;
   TargetDataMIPS32 &operator=(const TargetDataMIPS32 &) = delete;
 
@@ skipping 27 matching lines @@
 protected:
   explicit TargetHeaderMIPS32(GlobalContext *Ctx);
 
 private:
   ~TargetHeaderMIPS32() = default;
 };
 
 } // end of namespace Ice
 
 #endif // SUBZERO_SRC_ICETARGETLOWERINGMIPS32_H