[Ada] Avoid crash for -gnatR -gnatc

[Ada] Avoid crash for -gnatR -gnatc

If the -gnatR -gnatc are both given, then the compiler crashes.  This
patch fixes that, and avoids printing the uncomputed sizes and
alignments that were causing the crash. (Previous versions of the
compiler printed incorrect values in such cases.)

gcc/ada/

	* repinfo.adb (List_Object_Info): Do not try to print values
	that have not been computed (and so are No_Uint).
	(Rep_Not_Constant): Reverse sense and change name to
	Compile_Time_Known_Rep. This makes the code at call sites a
	little more readable. Simplify code to a single return
	statement.