[qfcc] Redo interface blocks as namespaces

There's no direct support for namespaces in Ruamoko yet, nor even in
qfcc, but glsl's blocks bring in a bit of foundation for them, even the
concept of "using" (for blocks with no instance name).

The members don't get locations allocated to them yet, but
fstrianglest.vert compiles and links correctly otherwise.

Also, there's no error checking yet.

tools/qfcc/source/expr_assign.c

@@ -107,6 +107,7 @@ is_lvalue (const expr_t *expr)
 				case sy_convert:
 					break;
 				case sy_macro:
+				case sy_namespace:
 					break;
 			}
 			break;