added comment

Author: ShyykoSerhiy

src/compiler/emitter.ts

@@ -4219,6 +4219,8 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, Promi
                 scopeEmitStart(node, "constructor");
                 increaseIndent();
                 if (ctor) {
+                    // Emit all the directive prologues (like "use strict").  These have to come before
+                    // any other preamble code we write (like parameter initializers).
                     var startIndex = emitDirectivePrologues(ctor.body.statements, /*startWithNewLine*/ true);                    
                     emitDetachedComments(ctor.body.statements);
                 }