* builtins.c: Include attribs.h and tree-nested.h.
        (expand_builtin): Implement targetm.calls.stdio_altname hook.
        * builtins.def (BUILT_IN_ASPRINTF): New builtin.
        * target.def (calls): Add stdio_altname.
        * doc/tm.texi.in: Add @hook TARGET_STDIO_ALTNAME.
        * doc/tm.texi: Regenerate.

        * config/avr/avr-protos.h (avr_stdio_altname): Prototype.
        * config/avr/avr.c (avr_stdio_altname): New function.
        (TARGET_STDIO_ALTNAME): Redefine.
        * config/avr/avr.h (LIB_SPEC): Add -lprintf_flt and -lscanf_flt.
        * config/avr/gen-avr-mmcu-specs.c (print_mcu) <*link>: Likewise.
	* config/avr/avr.h (POINTERS_EXTEND_UNSIGNED): Define.