nir: Simplify feq(fneg(a), a)) -> feq(a, 0.0)
nir: Simplify feq(fneg(a), a)) -> feq(a, 0.0)

The positive and negative value of a float can only
be equal to each other if it is -0.0f and 0.0f.
This is safe for Nan and Inf, as -Nan != Nan, and -Inf != Inf
This gives no changes in my shader-db

Signed-off-by: Thomas Helland <ca565e508460f734dd9d29a6ab6bd7e0e3ccde1d@gmail.com>
Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler