[Ada] Integer promotion for unary operators

[Arnaud Charlet <charlet at adacore dot com>]

This change fixes and extends the circuitry responsible for promotion of
operands to Integer when a conversion to Integer of an arithmetic operation
involving shorter integer types is encountered. (This early conversion helps
avoiding some overflow cases). After this change, the unary minus and
absolute value operators are included in this processing.

The following compilation must produce the displayed expanded code:

$ gcc -c -gnatG proc.adb
Source recreated from tree for Proc (body)
------------------------------------------


procedure proc (x : short_integer; y : short_integer) is
   z : integer;
begin
   z := integer(integer(x) + integer(y));
   z := integer(-integer(x));
   z := integer(abs integer(x));
   return;
end proc;

procedure Proc (X, Y : Short_Integer) is
   Z : Integer;
begin
   Z := Integer (X + Y);
   Z := Integer (-X);
   Z := Integer (abs X);
end Proc;

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

2009-10-28  Thomas Quinot  <quinot@adacore.com>

	* exp_ch4.adb (Expand_N_Type_Conversion): Perform Integer promotion for
	the operand of the unary minus and ABS operators.

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