Subzero: Fix ODR errors in the g++ build.

src/IceInstMIPS32.h

Index: src/IceInstMIPS32.h
diff --git a/src/IceInstMIPS32.h b/src/IceInstMIPS32.h
index 3037167ade4a9960735fca7ea58c4845b59f8182..25b48b5057e865bfd4eb2808f10706426c438eae 100644
--- a/src/IceInstMIPS32.h
+++ b/src/IceInstMIPS32.h
@@ -514,6 +514,17 @@ private:
   Variable *DestHi = nullptr;
 };
 
+// Declare partial template specializations of emit() methods that already have
+// default implementations. Without this, there is the possibility of ODR
+// violations and link errors.
+
+template <> void InstMIPS32Mflo::emit(const Cfg *Func) const;
+template <> void InstMIPS32Mfhi::emit(const Cfg *Func) const;
+template <> void InstMIPS32Mtlo::emit(const Cfg *Func) const;
+template <> void InstMIPS32Mthi::emit(const Cfg *Func) const;
+template <> void InstMIPS32Mult::emit(const Cfg *Func) const;
+template <> void InstMIPS32Multu::emit(const Cfg *Func) const;
+
 } // end of namespace MIPS32
 } // end of namespace Ice