nir/glsl: Emit abs, neg, and sat operations instead of source modifiers
nir/glsl: Emit abs, neg, and sat operations instead of source modifiers

Reviewed-by: Connor Abbott <71178acffcc112b21e5858656e5751f5e4aa9364@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler