* config/mips/xm-makeva.h: New file implements va_list alignment

	* config/mips/xm-makeva.h:  New file implements va_list alignment
	restrictions for mips hosts.
	* config/mips/{xm-irix3.h, xm-mips.h, xm-news-mips.h, xm-riscos.h}:
	Use it.
	* mips-tdep.c (init_extra_frame_info):  Do not check for
	mips_in_lenient_prologue if it is a dummy frame.