[Ada] Small enhancement to the -gnatD/-gnatG output for fixed-point types

[Ada] Small enhancement to the -gnatD/-gnatG output for fixed-point types

This is a small enhancement to the -gnatD/-gnatG output: the base type
of fixed-point types, which is usually an itype, used to be printed as
??? in this case.  It is now printed in a similar fashion as the first
subtype.

For the following package:

package P is

  type D is delta 128.0 / (2 ** 15) range 0.0 .. 256.0;

end P;

the  -gnatD/-gnatG must now be:

Source recreated from tree for P (spec)
---------------------------------------

p_E : short_integer := 0;

package p is
   type p__d is delta [1.0/256.0] range 0.0 .. 256.0;
   [type p__TdB is delta [1.0/256.0] range -[2147483648.0*2**(-8)] ..
     [2147483647.0*2**(-8)]]
   freeze p__TdB []
end p;

2019-07-22  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* sprint.adb (Sprint_Node_Actual)
	<N_Decimal_Fixed_Point_Definition>: Swap a couple of spaces.
	(Write_Itype): Minor consistency fixes throughout.  Add support
	for printing ordinary and decimal fixed-point types and
	subtypes.

From-SVN: r273689