ada: Enforce strict alignment for array types with aliased component

ada: Enforce strict alignment for array types with aliased component

This was initially implemented as part of AI12-001 but immediately disabled
because it breaks Florist on 32-bit platforms.  However, it is possible to
reenable it in almost all cases without affecting Florist, and the -gnatd_l
switch can now be used to disable it again.

gcc/ada/
	* debug.adb (d_l): Document new usage for the compiler.
	* freeze.adb (Check_Strict_Alignment): Set the Strict_Alignment
	flag on array types with aliased component, except if the
	component size is equal to the storage unit or the -gnatd_l switch
	is specified.