[Ada] Eliminate trampolines from GNAT tools

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk.

Eliminate features that cause trampolines to be generated (on some targets)
from GNAT tools and runtimes. This is done by making Check_Version_And_Help
into a generic (instead of passing a pointer-to-procedure parameter), and by
using the generic Heap_Sort_G instead of Heap_Sort_A. Also changing
GNAT.Command_Line.For_Each_Simple_Switch to be generic.

2007-12-13  Bob Duff  <duff@adacore.com>

	* clean.adb (Usage): Add line for -aP
	(Check_Version_And_Help): Change Check_Version_And_Help to be generic,
	with a parameter "procedure Usage", instead of passing a pointer to a
	procedure. This is to eliminate trampolines (since the Usage procedure
	is often nested in a main procedure, and it would be inconvenient to
	unnest it).

	* g-comlin.adb (For_Each_Simple_Switch): Change For_Each_Simple_Switch
	to be generic, with a parameter "procedure Callback (...)", instead of
	passing a pointer to a procedure. This is to eliminate trampolines
	(since the Callback procedure is usually nested).

	* gnatfind.adb, switch.adb, switch.ads, gnatlink.adb, gnatls.adb, 
	gnatname.adb, gnatxref.adb, gnatchop.adb, gprep.adb, gnatbind.adb
	(Check_Version_And_Help): Change Check_Version_And_Help to be generic.

	* g-pehage.adb (Compute_Edges_And_Vertices, Build_Identical_Key_Sets):
	Use the generic Heap_Sort_G instead of Heap_Sort_A.

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