Added comment on reason for method being public

Author: cedihegi

compiler/rustc_mir_transform/src/lib.rs

@@ -431,6 +431,8 @@ fn mir_drops_elaborated_and_const_checked(tcx: TyCtxt<'_>, def: LocalDefId) -> &
     tcx.alloc_steal_mir(body)
 }
 
+// Made public such that `mir_drops_elaborated_and_const_checked` can be overridden
+// by custom rustc drivers, running all the steps by themselves.
 pub fn run_analysis_to_runtime_passes<'tcx>(tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
     assert!(body.phase == MirPhase::Analysis(AnalysisPhase::Initial));
     let did = body.source.def_id();