ada: Do not use ATTR_ADDR_EXPR for 'Unrestricted_Access

ada: Do not use ATTR_ADDR_EXPR for 'Unrestricted_Access

Unlike for 'Access or 'Unchecked_Access, the Attribute_to_gnu routine passes
ATTR_ADDR_EXPR to build_unary_op for 'Unrestricted_Access, which causes the
processing done in build_unary_op to flatten the reference, in particular to
remove all intermediate (view) conversions, which may be problematic for the
SUBSTITUTE_PLACEHOLDER_IN_EXPR machinery.

gcc/ada/ChangeLog:

	* gcc-interface/trans.cc (Attribute_to_gnu) <Attr_Access>: Do not
	pass ATTR_ADDR_EXPR to build_unary_op for 'Unrestricted_Access.