ShaderChunk: Fixed MeshPhongMaterial breakage. See #12484

src/renderers/shaders/ShaderChunk/tonemapping_pars_fragment.glsl

@@ -1,3 +1,7 @@
+#ifndef saturate
+	#define saturate(a) clamp( a, 0.0, 1.0 )
+#endif
+
 uniform float toneMappingExposure;
 uniform float toneMappingWhitePoint;