Fixes Ori and the Blind Forest's menu on GLASM. For some reason
(probably high level optimizations) it is not sanitized on SPIR-V for
OpenGL. Vulkan is unaffected by this change.

Fixes ubsan issue.

Add Intel Xe support.

Causes regressions on Bowser's Fury.

Add support for null registers. These are used when an instruction has
no usages.

This comes handy when an instruction is only used for its CC value, with
the caveat of having to invalidate all pseudo-instructions before
defining the instruction itself in the register allocator. This commits
changes this.

Workaround a bug on Nvidia's condition codes conditional execution using
branches.