re PR target/65296 ([avr] fix various issues with specs file generation)

re PR target/65296 ([avr] fix various issues with specs file generation)

	PR target/65296
	* config/avr/avr.opt (-nodevicelib): New option.
	* doc/invoke.texi (AVR Options): Document it.
	* config/avr/avrlibc.h (LIB_SPEC, LIBGCC_SPEC) [avr1]: Don't link
	libgcc.a, libc.a, libm.a.
	* config/avr/specs.h: Same.
	* config/avr/gen-avr-mmcu-specs.c (print_mcu): Don't print specs
	which don't (directly) depend on the device.  Print more help.
	(*avrlibc_devicelib) [-nodevicelib]: Don't link libdev.a.
	(*cpp): Don't define __AVR_DEV_LIB_NAME__.
	* config/avr/driver-avr.c: Remove -nodevicelib from option list in
	case of an error.
	(avr_devicespecs_file): Use suffix "%s" instead of absolute path
	for specs file name.
	* config/avr/avr-arch.h (avr_mcu_t) [.library_name]: Remove.
	* config/avr/avr-mcus.def: Adjust initializers and comments.

From-SVN: r221475