Fix PR ada/101970

This is a regression present on the mainline and 11 branch in the form of an
ICE for an enumeration type with a full signed representation for its size.

	PR ada/101970
	* exp_attr.adb (Expand_N_Attribute_Reference) <Attribute_Enum_Rep>:
	Use an unchecked conversion instead of a regular conversion in the
	enumeration case and remove Conversion_OK flag in the integer case.
	<Attribute_Pos>: Remove superfluous test.

	* gnat.dg/enum_rep2.adb: New test.
2 files changed