PR middle-end/91490 - bogus argument missing terminating nul warning on strlen of a flexible array member

gcc/c-family/ChangeLog:

	PR middle-end/91490
	* c-common.c (braced_list_to_string): Add argument and overload.
	Handle flexible length arrays and unions.

gcc/testsuite/ChangeLog:

	PR middle-end/91490
	* c-c++-common/Warray-bounds-7.c: New test.
	* gcc.dg/Warray-bounds-39.c: Expect either -Warray-bounds or
	-Wstringop-overflow.
	* gcc.dg/strlenopt-78.c: New test.

gcc/ChangeLog:

	PR middle-end/91490
	* builtins.c (c_strlen): Rename argument and introduce new local.
	Set no-warning bit on original argument.
	* expr.c (string_constant): Pass argument type to fold_ctor_reference.
	Fold empty and zero constructors into empty strings.
	* gimple-fold.c (fold_nonarray_ctor_reference): Return a STRING_CST
	for missing initializers.
	* tree.c (build_string_literal): Handle optional argument.
	* tree.h (build_string_literal): Add defaulted argument.
	* gimple-ssa-warn-restrict.c (maybe_diag_access_bounds): Check
	no-warning bit on original expression.

From-SVN: r274837