Replace constant values 8 to 15 by AMD64_R8_REGNUM to
	AMD64_R15_REGNUM when a register index is expected.
	* amd64-windows-tdep.c (amd64_windows_dummy_call_integer_regs):
	Substitute in array.
	* amd64-tdep.c (amd64_dwarf_regmap): Ditto.
	(amd64_push_arguments): Substitute in integer_regnum array.