ada: Restrict previous change made to expansion of allocators

There is no need to build a cleanup if exceptions cannot be propagated.

gcc/ada/ChangeLog:

	* exp_ch4.adb (Expand_Allocator_Expression): Do not build a cleanup
	if restriction No_Exception_Propagation is active.
	* exp_ch6.adb (Make_Build_In_Place_Call_In_Allocator): Likewise.