re PR tree-optimization/93210 (Sub-optimal code optimization on struct/combound constexpr (gcc vs. clang))

	PR tree-optimization/93210
	* fold-const.h (native_encode_initializer,
	can_native_interpret_type_p): Declare.
	* fold-const.c (native_encode_string): Fix up handling with off != -1,
	simplify.
	(native_encode_initializer): New function, moved from dwarf2out.c.
	Adjust to native_encode_expr compatible arguments, including dry-run
	and partial extraction modes.  Don't handle STRING_CST.
	(can_native_interpret_type_p): No longer static.
	* gimple-fold.c (fold_ctor_reference): For native_encode_expr, verify
	offset / BITS_PER_UNIT fits into int and don't call it if
	can_native_interpret_type_p fails.  If suboff is NULL and for
	CONSTRUCTOR fold_{,non}array_ctor_reference returns NULL, retry with
	native_encode_initializer.
	(fold_const_aggregate_ref_1): Formatting fix.
	* dwarf2out.c (native_encode_initializer): Moved to fold-const.c.
	(tree_add_const_value_attribute): Adjust caller.

	* gcc.dg/pr93210.c: New test.
	* g++.dg/opt/pr93210.C: New test.

From-SVN: r280141