[Ada] Implement Ada 2012 AI-0177 Parametrized Expressions

[Arnaud Charlet <charlet at adacore dot com>]

This patch implements the new Ada 2012 notion of parametrized
expressions. The form is FUNCTION SPECIFICATION IS EXPRESSION.
This is equivalent to the corresponding function body that
returns the expression, but it can appear in a package spec.
The following compiles clean with -gnat2012 and outputs 102.

package ParamExpr is
   F : Integer := 1;
   function Squarep1 (A : Integer) return Integer is A * A + F;
end;

with ParamExpr; use ParamExpr;
with Text_IO; use Text_IO;
procedure ParamExprM is
begin
   F := 2;
   Put_Line (Squarep1 (10)'Img);
end ParamExprM;

Tested on x86_64-pc-linux-gnu, committed on trunk

2010-10-07  Robert Dewar  <dewar@adacore.com>

	* exp_util.adb (Insert_Actions): Add handling of
	N_Parametrized_Expression.
	* par-ch6.adb (P_Subprogram): Add parsing of parametrized expression
	* sem.adb: Add entry for N_Parametrized_Expression
	* sem_ch6.adb (Analyze_Parametrized_Expression): New procedure
	* sem_ch6.ads (Analyze_Parametrized_Expression): New procedure
	* sinfo.ads, sinfo.adb: Add N_Parametrized_Expression
	* sprint.adb (Sprint_Node): Add handling for N_Parametrized_Expression

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