The node being processed may be removed from the list and put in a
different list. Not using the safe version caused list processing to
change streams after moving a node.
For the shader containing 'main', use the linked shader (i.e., the
clone of the original shader that contained main) as the source for
global instructions to move into main.
Find instructions in all shaders that are not contained in a function
(i.e., initializers for global variables). "Move" these instructions
to the top of the main function in the linked shader. As a
side-effect, many global variables will also be copied into the linked
shader.
This currently involves an ugly hack so that every link doesn't result
in all the built-in functions showing up as multiply defined. As soon
as the built-in functions are stored in a separate compilation unit,
ir_function_signature::is_built_in can be removed.
Uses of the bits for allocation are offset by 16, and
VERT_BIT_GENERIC0 already has the 16 offset. As a result, it was
preventing the wrong thing from being allocated.
