Add initial prototype.

3-mid/opengl/source/platform/glx/private/thin/glx-context.ads

@@ -0,0 +1,14 @@
+with
+     glx.Pointers;
+
+package glx.Context
+is
+   subtype Item is Pointers.ContextRec_Pointer;
+
+   type Pointer         is access all Item;
+   type Pointer_Pointer is access all Pointer;
+
+   type Items    is array (C.size_t range <>) of aliased Item;
+   type Pointers is array (C.size_t range <>) of aliased Pointer;
+
+end glx.Context;