Fix various problems with specs file generation.

Fix various problems with specs file generation.

gcc/
	Fix various problems with specs file generation.
	PR target/65296
	* config.gcc (extra_gcc_objs) [avr]: Remove.
	* config/avr/driver-avr.c: Remove file.
	* config/avr/t-avr (driver-avr.o): Remove rule.
	(gen-avr-mmcu-specs): Use CXX_FOR_BUILD, CXXFLAGS_FOR_BUILD and
	INCLUDES to build.  Depend on TM_H.
	* config/avr/gen-avr-mmcu-specs.c: Tidy up code.  Fix various
	build warnings.  Fix non-matching types and non-existing %-codes.
	(tm.h): Include.
	(*lib) [!WITH_AVRLIBC]: Don't link libdev.a.
	(*libgcc) [WITH_AVRLIBC]: Add "-lm".
	* config/avr/avrlibc.h (LIBGCC_SPEC): Remove definition.
	* config/avr/avr.h (DRIVER_SELF_SPECS): Fix handling of -march=.
	(CPP_SPEC, CC1PLUS_SPEC, ASM_SPEC, LINK_SPEC, LIB_SPEC)
	(LIBGCC_SPEC): Remove definitions.

From-SVN: r221141