glsl: Use ir_builder more in opt_algebraic.

glsl: Use ir_builder more in opt_algebraic.

While ir_builder is slightly less efficient, we're only increasing the
work when there's actual optimization being done, and it's way more
readable code.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>