xtensa.c (xtensa_build_va_list): Use lang_hooks.types.make_type instead of make_node...

xtensa.c (xtensa_build_va_list): Use lang_hooks.types.make_type instead of make_node; set up __va_list_tag type decl.

        * config/xtensa/xtensa.c (xtensa_build_va_list): Use
        lang_hooks.types.make_type instead of make_node; set up
        __va_list_tag type decl.
        (xtensa_builtin_saveregs): Remove broken use of
        RTX_UNCHANGING_P and unnecessary use of MEM_IN_STRUCT_P
        for saved registers; add varargs alias set.

From-SVN: r54288