[Ada] Unnesting: refactor handling of uplevel refs. for unconstrained arrays

[Ada] Unnesting: refactor handling of uplevel refs. for unconstrained arrays

2018-06-11  Ed Schonberg  <schonberg@adacore.com>

gcc/ada/

	* exp_unst.ads, exp_unst.adb (Needs_Fat_Pointer,
	Build_Access_Type_Decl): New subprograms to handle uplevel references
	to formals of an unconstrained array type. The activation record
	component for these is an access type, and the reference is rewritten
	as an explicit derefenrence of that component.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@261425 138bc75d-0d04-0410-961f-82ee72b054a4