Implement attribute progmem on reduced Tiny cores by adding flash offset 0x4000 to respective symbols.

gcc/
	Implement attribute progmem on reduced Tiny cores by adding
	flash offset 0x4000 to respective symbols.

	PR target/71948
	* doc/extend.texi (AVR Variable Attributes) [progmem]: Add
	documentation how it works on reduced Tiny cores.
	(AVR Named Address Spaces): No support for reduced Tiny.
	* config/avr/avr.c (AVR_SYMBOL_FLAG_TINY_PM): New macro.
	(avr_address_tiny_pm_p): New static function.
	(avr_print_operand_address) [AVR_TINY]: Add AVR_TINY_PM_OFFSET
	if the address is in progmem.
	(avr_assemble_integer): Same.
	(avr_encode_section_info) [AVR_TINY]: Set AVR_SYMBOL_FLAG_TINY_PM
	for symbol_ref in progmem.
	* config/avr/avr.h (AVR_TINY_PM_OFFSET): New macro.
	* config/avr/avr-c.c (avr_cpu_cpp_builtins): Use it instead of
	magic 0x4000 when built-in def'ing __AVR_TINY_PM_BASE_ADDRESS__.
gcc/testsuite/
	PR target/71948
	* gcc.target/avr/torture/tiny-progmem.c: New test.

From-SVN: r238525