* x86-64-tdep.c (x86_64_push_arguments): Always set %rax to number

	* x86-64-tdep.c (x86_64_push_arguments): Always set %rax to number
	of SSE registers so that varargs functions work.  Rework handling
	of passing arguments on the stack.
	(x86_64_store_return_value): Return double and float values in SSE
	register.