[Ada] Project file improvements

[Arnaud Charlet <charlet at adacore dot com>]

Tested on i686-linux, committed on trunk

A new switch is added to the GNAT project-aware tools: gnatmake,
gnatclean, gnatname and the gnat driver. When --subdirs=<subdir> is
specified, the actual directories (except the source directories) are
subdirectories of the directories specified in the project files.
If they do not exist, they are created automatically by the tool.

The test for this is to call gnatmake with --subdirs=xref: the object
files and the ALI files should be located in a subdirectory of the object
directory declared in the project.

Also, gnatmake can be called with switch -eL to follow symbolic links when
processing project files. This patch add this same switch to gnatclean,
so that it can process successfully project trees with symbolic links
for the project files.
The test for this is to call gnatclean with switch -eL.

Then, gnatmake -s should ckeck only switches that are passed to gnat1 by the
gcc driver and that are stored in the ALI file by gnat1. This patch
ensures that this is the case.

The test for this is to invoke twice:
   gnatmake -s main.adb -cargs -pipe -time
No recompilation should occurs for the second invocation.

Finally, project files can now be qualified before the reserved word "project".
Allowed qualifiers are:
  standard: a standard project cannot be a library project or an abstract
            project
  library: a library project need to have attribute Library_Name and
           Library_Dir declared
  abstract: an abstract project is one where it is declared that there
            are no sources
  configuration: a configuration project is only allowed as a
                 configuration file for gprbuild/gprclean

In addition two more qualifiers "aggregate" and "aggregate library" are
recognized for future extension of the project manager.

2008-04-08  Vincent Celier  <celier@adacore.com>

	* clean.adb (Parse_Cmd_Line): Recognize switch --subdirs=
	(Usage): Add line for switch --subdirs=
	Add new switch -eL, to follow symbolic links when processing project
	files.

	* gnatcmd.adb: Process switches -eL and --subdirs=
	(Non_VMS_Usage): Output "gnaampcmd" instead of "gnat", and call
	Program_Name to get proper tool names when AAMP_On_Target is set.
	(Gnatcmd): Call Add_Default_Search_Dirs and Get_Target_Parameters to get
	AAMP_On_Target set properly for use of GNAAMP tools (this is needed by
	Osint.Program_Name).

	* gnatname.adb: (Scan_Args): Recognize switches -eL and --subdirs=
	(Usage): Add lines for switches -eL and --subdirs=

	* makeusg.adb: Add line for switch --subdirs=

	* prj.ads: 
	(Source_Data): New Boolean component Compiled, defaulted to True
	(Empty_File_Name: New global variable in private part, initialized in
	procedure Initialize.
	(Subdirs_Option): New constant string
	(Subdirs): New String_Ptr global variable
	(Language_Config): New component Include_Compatible_Languages
	(Project_Qualifier): New type for project qualifiers
	(Project_Data): New component Qualifier
	(Project_Configuration): New component Archive_Builder_Append_Option

	* prj-nmsc.adb (Get_Unit_Exceptions): When a unit is already in
	another imported project indicate the name of this imported project.
	(Check_File): When a unit is in two project files, indicate the project
	names and the paths of the source files for each project.
	(Add_Source): Set Compiled to False if compiler driver is empty. Only
	set object, dependency and switches file names if Compiled is True.
	(Process_Compiler): Allow the empty string for value of attribute Driver
	(Get_Directories): When Subdirs is not null and Object_Dir is not
	 specified, locate and create if necessary the actual object dir.
	(Locate_Directory): When Subdirs is not empty and Create is not the
	empty string, locate and create if necessary the actual directory
	as a subdirectory of directory Name.
	(Check_Library_Attributes.Check_Library): Allow a project where the only
	"sources" are header files of file based languages to be imported by
	library projects, in multi-language mode (gprbuild).
	(Check_Library_Attributes.Check_Library): In multi-language mode
	(gprbuild), allow a library project to import a project with no
	sources, even when this is not declared explicitly.
	(Check_If_Externally_Built): A virtual project extending an externally
	built project is also externally built.
	(Check_Library_Attributes): For a virtual project extending a library
	project, inherit the library directory.
	(Process_Project_Level_Array_Attributes): Process new attribute
	Inherit_Source_Path.
	For projects with specified qualifiers "standard", "library" or
	"abstract", check that the project conforms to the qualifier.
	(Process_Project_Level_Simple_Attributes): Process new attribute
	 Archive_Builder_Append_Option.

	* switch-m.adb: (Scan_Make_Switches): Process switch --subdirs=
	(Normalize_Compiler_Switches): Only keep compiler switches that are
	passed to gnat1 by the gcc driver and that are stored in the ALI file
	by gnat1.
	Do not take into account switc -save-temps

	* makegpr.adb (Compile_Link_With_Gnatmake): Transmit switch -eL if
	gprmake is called with -eL.
	(Scan_Arg): Recognize switch -eL
	(Usage): Add line for switch -eL

	* prj.adb (Initialize): Initialize Empty_File_Name
	(Project_Empty): New component Qualifier

	* prj-attr.ads, prj-attr.adb: New project level attribute
	Inherit_Source_Path.
	New project level attribute Archive_Builder_Append_Option

	* prj-dect.adb: Replace System.Strings by GNAT.Strings.

	* prj-ext.adb (Initialize_Project_Path): In Multi_Language mode, add
	<prefix>/lib/gnat in the project path, after <prefix>/share/gpr, for
	upward compatibility.

	* prj-part.adb (Project_Path_Name_Of.Try_Path): In high verbosity, put
	each Trying ..." on different lines.
	(Parse_Single_Project): Recognize project qualifiers. Fail in qualifier
	is "configuration" when not in configuration. Fail when in configuration
	when a specified qualifier is other than "configuration".

	* prj-proc.adb (Process_Declarative_Items): Link new elements of copied
	full associative array together.
	(Recursive_Process): Put the project qualifier in the project data
	
	* prj-tree.ads, prj-tree.adb: (Project_Qualifier_Of): New function
	(Set_Project_Qualifier_Of): New procedure

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