Fix miscompilation of predicate on bit-packed array types

Fix miscompilation of predicate on bit-packed array types

This is a regression present on the mainline and 11 branch in the form of a
miscompilation by the new mod/ref IPA pass of code that passes constrained
bit-packed array objets in a call to a subprograms taking unconstrained
bit-packed array parameters, which occurs for predicate on bit-packed array
types for example.

gcc/ada/
	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Array_Type>: Add PAT
	local constant and use it throughout.  If it is set, use a ref-all
	pointer type for the pointer-to-array field of the fat pointer type.
	<E_Array_Subtype>: Add PAT local constant and use it throughout.
gcc/testsuite/
	* gnat.dg/bit_packed_array6.adb: New test.
	* gnat.dg/bit_packed_array6_pkg.ads: New helper.