sim: v850: reduce extra header inclusion to igen files

Limit these extra header includes to only when specific igen files
include us until we can move the includes to the igen fils directly.

sim/v850/sim-main.h

@@ -8,7 +8,11 @@
  * TODO: Move these includes to the igen files that need them.
  * This requires extending the igen syntax to support header includes.
  */
+#if defined(SEMANTICS_C) || defined(SUPPORT_C)
 #include "sim-signal.h"
+#endif
+#if defined(ENGINE_C) || defined(IDECODE_C) || defined(SEMANTICS_C)
 #include "v850-sim.h"
+#endif
 
 #endif