Makes codegen from typical D3D emulation SPIR-V more readable.
Also makes cross compilation with NotEqual more sensible.
It's very rare to actually need the strict NaN-checks in practice.
Also, glslang now emits UnordNotEqual by default it seems, so give up
trying to assume OrdNotEqual. Harmonize for UnordNotEqual as the sane
default.
There is no direct way to express this, so invert boolean results to
force any NaN -> true. glslang emits Ordered compare instructions
everywhere, and the GLSL spec is not clear on this, so assume this is
fine.
