backport: re PR target/80462 ([avr] Incorrect "warning: uninitialized variable 'xxx...

backport: re PR target/80462 ([avr] Incorrect "warning: uninitialized variable 'xxx' put into program memory area" for identical strings)

gcc/
	Backport from 2017-04-19 trunk r246997.
	PR target/80462
	* config/avr/avr.c (tree.h): Include it.
	(hash-table.h): Include it.
	(hash-set.h): Include it.
	(symtab.h): Include it.
	(inchash.h): Include it.
	(function.h): Include it.
	(hash-map.h): Include it.
	(plugin-api.h): Include it.
	(ipa-ref.h): Include it.
	(cgraph.h): Include it.
	(avr_encode_section_info): Don't warn for uninitialized progmem
	variable if it's just an alias.

	Backport from 2017-07-12 trunk r250151.
	PR target/81407
	* config/avr/avr.c (avr_encode_section_info)
	[progmem && !TREE_READONLY]: Error if progmem object needs
	constructing.

From-SVN: r251267