sim m32c: Include defs.h in m32c.opc and r8c.opc.

gnulib can override stdio.h and/or stdlib.h in which case the gnulib
headers require config.h to be included first.

gdb/sim/m32c/ChangeLog:

	* m32c.opc: Include defs.h.
	* r8c.opc: Likewise.