re PR c/83801 ([avr] String constant in __flash not put into .progmem)

re PR c/83801 ([avr] String constant in __flash not put into .progmem)

	PR c/83801
	* c-tree.h (decl_constant_value_1): Add a bool argument.
	* c-typeck.c (decl_constant_value_1): Add IN_INIT argument, allow
	returning a CONSTRUCTOR if it is true.  Use error_operand_p.
	(decl_constant_value): Adjust caller.
	* c-fold.c (c_fully_fold_internal): If in_init, pass true to
	decl_constant_value_1 as IN_INIT.  Otherwise, punt if
	decl_constant_value returns initializer that has BLKmode or
	array type.
	(c_fully_fold_internal) <case COMPONENT_REF>: Fold if !lval.

	* gcc.dg/pr83801.c: New test.

From-SVN: r256608