nir: Recognize trivial min/max.
nir: Recognize trivial min/max.

No changes, but does prevent some regressions in the next commit.

Reviewed-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
Reviewed-by: Glenn Kennard <feea5431f8695a3af7470d472cb16ac8e02bab01@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler