Initial support for Target (cross-compiling)

index/native/alire-index-gnat.ads

@@ -4,7 +4,11 @@ package Alire.Index.GNAT is
      ("GNAT is a compiler for the Ada programming language");
 
    Base : constant Release := Project.Unreleased
-     (Properties => Path ("/usr/bin"));
+     (Properties =>
+        Path ("/usr/bin"),
+
+      Available_When =>
+        Target = Native);
 
    --  If minor versions proved important they could be segregated with platform-specific knowledge
 

src/alire-index.ads

@@ -244,6 +244,7 @@ package Alire.Index is
    use all type Licensing.Licenses;
    use all type Platforms.Compilers;
    use all type Platforms.Operating_Systems;
+   use all type Platforms.Targets;
    use all type Platforms.Versions;
    use all type Platforms.Word_Sizes;
    use all type Properties.Property'Class;
@@ -328,11 +329,14 @@ package Alire.Index is
    use all type Requisites.Platform.Distributions.Comparable;
 
    function Operating_System is new Requisites.Platform.Op_Systems.Factory;
-   use all type Requisites.Platform.Op_Systems.Comparable;  
+   use all type Requisites.Platform.Op_Systems.Comparable;     
    
    function Distro_Release is new Requisites.Platform.Versions.Factory;
    use all type Requisites.Platform.Versions.Comparable;
    
+   function Target is new Requisites.Platform.Targets.Factory;
+   use all type Requisites.Platform.Targets.Comparable;
+   
    function Word_Size is new Requisites.Platform.Word_Sizes.Factory;
    use all type Requisites.Platform.Word_Sizes.Comparable;
 

src/alire-platforms.ads

@@ -18,6 +18,10 @@ package Alire.Platforms with Preelaborate is
                               Windows,
                               OS_Unknown);
 
+   type Targets is (Native,
+                    Unknown_Cross_Target);
+   --  Minimal preparations for cross-compiling
+
    type Distributions is (Debian,
                           Ubuntu,
                           Distro_Unknown);

src/alire-properties-platform.ads

@@ -13,6 +13,9 @@ package Alire.Properties.Platform with Preelaborate is
    package Operating_Systems is new Values (Platforms.Operating_Systems,
                                             Platforms.Operating_Systems'Image);
 
+   package Targets is new Values (Platforms.Targets,
+                                  Platforms.Targets'Image);
+
    package Versions is new Values (Platforms.Versions,
                                    Platforms.Versions'Image);
 
@@ -26,6 +29,8 @@ package Alire.Properties.Platform with Preelaborate is
 
    function System_Is (OS : Platforms.Operating_Systems) return Vector renames Operating_Systems.New_Vector;
 
+   function Target_Is (T : Platforms.Targets) return Vector renames Targets.New_Vector;
+
    function Version_Is (V : Platforms.Versions) return Vector renames Versions.New_Vector;
 
    function Word_Size_Is (V : Platforms.Word_Sizes) return Vector renames Word_Sizes.New_Vector;

src/alire-requisites-platform.ads

@@ -48,6 +48,12 @@ package Alire.Requisites.Platform with Preelaborate is
    package Distribution_Cases_Props is new Conditional.For_Properties.Case_Statements
      (Ps.Distributions, Distributions.Is_Equal_To);
 
+   package Targets is new Comparables
+     (Ps.Targets, Ps."<", Ps.Targets'Image,
+      PrPl.Targets.Property,
+      PrPl.Targets.Element,
+      "Target");
+
    package Versions is new Comparables
      (Ps.Versions, Ps."<", Ps.Versions'Image,
       PrPl.Versions.Property,