Error if profiling disabled and -pprof specifed.

rtiow/src/bin/tracer.rs

@@ -97,6 +97,9 @@ fn main() -> Result<(), std::io::Error> {
     let opt = Opt::from_args();
     let scene = opt.model.scene(&opt);
     fs::create_dir_all(&opt.output)?;
+    if opt.pprof.is_some() && !cfg!(feature = "profile") {
+        panic!("profiling disabled at compile time, but -pprof specified");
+    }
     if let Some(ref pprof_path) = opt.pprof {
         PROFILER
             .lock()