Making GLSL AST nodes while preserving lineno info

Eventually we will need some way to locate an identifier's
definition, so add "lineno" to each AST node.  May want to
change this to "position" later.  The makeAstNode<T>() function
takes care of automatically decorating nodes with line numbers.

src/libs/glsl/glslast.h

@@ -70,10 +70,10 @@ class GLSL_EXPORT List: public Managed
 {
 public:
     List(const T &value)
-        : value(value), next(this) {}
+        : value(value), next(this), lineno(0) {}
 
     List(List *previous, const T &value)
-        : value(value)
+        : value(value), lineno(0)
     {
         next = previous->next;
         previous->next = this;
@@ -88,6 +88,7 @@ public:
 
     T value;
     List *next;
+    int lineno;
 };
 
 // Append two lists, which are assumed to still be circular, pre-finish.