Fix internal error on locally derived bit-packed array type

This is a regression present on the mainline, 11 and 10 branches,
in the form of an ICE on a locally derived bit-packed array type.

gcc/ada/
	* gcc-interface/decl.c (gnat_to_gnu_entity) <E_Array_Type>: Process
	the implementation type of a packed type implemented specially.
gcc/testsuite/
	* gnat.dg/derived_type7.adb, gnat.dg/derived_type7.ads: New test.
3 files changed