Explain why we don't set --sysroot if --print is passed by the caller

Author: oli-obk

cargo-miri/bin.rs

@@ -871,6 +871,7 @@ fn phase_rustc(mut args: env::Args, phase: RustcPhase) {
             cmd.arg("-C").arg("panic=abort");
         }
     } else {
+        // For host crates (but not when we are printing), we might still have to set the sysroot.
         if !print {
             // When we're running `cargo-miri` from `x.py` we need to pass the sysroot explicitly as rustc
             // can't figure out the sysroot on its own unless it's from rustup.