glsl: Optimize scalar all_equal/any_nequal into equal/nequal.
glsl: Optimize scalar all_equal/any_nequal into equal/nequal.

Cuts an instruction from two shaders in Tesseract, by allowing the
(x+y) cmp 0 -> x cmp -y optimization to take place.

instructions in affected programs:     1198 -> 1194 (-0.33%)

Reviewed-by: Eric Anholt <96f164ad4d9b2b0dacf8ebee2bb1eeb3aa69adf1@anholt.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler