nir/algebraic: Only include nir_search_helpers once
nir/algebraic: Only include nir_search_helpers once

We were including it once per value, so probably around 10k times.
Let's not cause the compiler any more work than we have to.

Reviewed-by: Iago Toral Quiroga <a847aabaac44184372f6b1cd1a59aa254daaeb0b@igalia.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler