Subzero: Fix build warnings/errors under g++.

src/IceTargetLoweringX8664.cpp

 //===- subzero/src/IceTargetLoweringX8664.cpp - x86-64 lowering -----------===//
 //
 //                        The Subzero Code Generator
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 ///
 /// \file
@@ skipping 70 matching lines @@
 };
 
 const size_t MachineTraits<TargetX8664>::TableTypeX8664AttributesSize =
     llvm::array_lengthof(TableTypeX8664Attributes);
 
 const uint32_t MachineTraits<TargetX8664>::X86_STACK_ALIGNMENT_BYTES = 16;
 const char *MachineTraits<TargetX8664>::TargetName = "X8664";
 
 template <>
 std::array<llvm::SmallBitVector, RCX86_NUM>
-    TargetX86Base<TargetX8664>::TypeToRegisterSet = {};
+    TargetX86Base<TargetX8664>::TypeToRegisterSet = {{}};
 
 template <>
 std::array<llvm::SmallBitVector,
            TargetX86Base<TargetX8664>::Traits::RegisterSet::Reg_NUM>
-    TargetX86Base<TargetX8664>::RegisterAliases = {};
+    TargetX86Base<TargetX8664>::RegisterAliases = {{}};
 
 template <>
 llvm::SmallBitVector
     TargetX86Base<TargetX8664>::ScratchRegs = llvm::SmallBitVector();
 
 } // end of namespace X86Internal
 
 //------------------------------------------------------------------------------
 //     __      ______  __     __  ______  ______  __  __   __  ______
 //    /\ \    /\  __ \/\ \  _ \ \/\  ___\/\  == \/\ \/\ "-.\ \/\  ___\
@@ skipping 859 matching lines @@
 // case the high-level table has extra entries.
 #define X(tag, sizeLog2, align, elts, elty, str)                               \
   static_assert(_table1_##tag == _table2_##tag,                                \
                 "Inconsistency between ICETYPEX8664_TABLE and ICETYPE_TABLE");
 ICETYPE_TABLE
 #undef X
 } // end of namespace dummy3
 } // end of anonymous namespace
 
 } // end of namespace Ice