sinfo.ads, sinfo.adb (Alloc_For_BIP_Return): New flag to indicate that an allocator came from a b-i-p return statement.

2017-10-20  Bob Duff  <duff@adacore.com>

	* sinfo.ads, sinfo.adb (Alloc_For_BIP_Return): New flag to indicate
	that an allocator came from a b-i-p return statement.
	* exp_ch4.adb (Expand_Allocator_Expression): Avoid adjusting the return
	object of a nonlimited build-in-place function call.
	* exp_ch6.adb (Expand_N_Extended_Return_Statement): Set the
	Alloc_For_BIP_Return flag on generated allocators.
	* sem_ch5.adb (Analyze_Assignment): Move Assert to where it can't fail.
	If the N_Assignment_Statement has been transformed into something else,
	then Should_Transform_BIP_Assignment won't work.
	* exp_ch3.adb (Expand_N_Object_Declaration): A previous revision said,
	"Remove Adjust if we're building the return object of an extended
	return statement in place." Back out that part of the change, because
	the Alloc_For_BIP_Return flag is now used for that.

From-SVN: r253940