Fix #121819: OpenColorIO GLSL error after recent change, only apply to Metal

intern/opencolorio/ocio_impl_glsl.cc

@@ -205,7 +205,9 @@ static bool createGPUShader(OCIO_GPUShader &shader,
   info.define("texture2D", "texture");
   info.define("texture3D", "texture");
   /* Work around unsupported in keyword in Metal GLSL emulation. */
+#ifdef __APPLE__
   info.define("in", "");
+#endif
   info.typedef_source("ocio_shader_shared.hh");
   info.sampler(TEXTURE_SLOT_IMAGE, ImageType::FLOAT_2D, "image_texture");
   info.sampler(TEXTURE_SLOT_OVERLAY, ImageType::FLOAT_2D, "overlay_texture");