Update the MSP430X/IAR port layer to support the medium data model.

Source/portable/IAR/MSP430X/data_model.h

@@ -61,14 +61,29 @@
 	#define pop_x pop.w
 	#define mov_x mov.w
 	#define cmp_x cmp.w
-#else /* DATA_MODEL_SMALL__ */
+#endif
+
+#ifdef __DATA_MODEL_MEDIUM__
+	#define pushm_x pushm.a
+	#define popm_x popm.a
+	#define push_x pushx.a
+	#define pop_x popx.a
+	#define mov_x mov.w
+	#define cmp_x cmp.w
+#endif
+
+#ifdef __DATA_MODEL_LARGE__
 	#define pushm_x pushm.a
 	#define popm_x popm.a
 	#define push_x pushx.a
 	#define pop_x popx.a
 	#define mov_x movx.a
 	#define cmp_x cmpx.a
-#endif /* __DATA_MODEL_SMALL__
+#endif
+
+#ifndef pushm_x
+	#error The assembler options must define one of the following symbols: __DATA_MODEL_SMALL__, __DATA_MODEL_MEDIUM__, or __DATA_MODEL_LARGE__
+#endif
 
 #endif /* DATA_MODEL_H */