Support for C++ constructors/destructors.

Support for C++ constructors/destructors.

	* config/avr/avr.c (avr_output_function_epilogue): Jump to exit()
	instead of looping if main() returns.
	(asm_file_start): Output global symbols that cause .data and .bss
	initialization code to be linked in, unconditionally for now.
	(avr_asm_out_ctor, avr_asm_out_dtor): New functions.
	* config/avr/avr.h (CTORS_SECTION_ASM_OP, DTORS_SECTION_ASM_OP): New.
	(TARGET_ASM_CONSTRUCTOR, TARGET_ASM_DESTRUCTOR): New.
	(LIBSTDCXX): New.
	* config/avr/libgcc.S (_exit): Split in .fini9 and .fini0 sections.
	(__tablejump__): New.
	(__do_copy_data, __do_clear_bss): New.
	(__do_global_ctors, __do_global_dtors): New.
	* config/avr/t-avr (LIB1ASMFUNCS): Add _copy_data, _clear_bss,
	_ctors, _dtors.

From-SVN: r54156