[NFC] Use the Correct const-Qualification in Dependency Code

T *const does not prevent logically non-const accesses to the underlying data, it merely indicates that the pointer value itself is const. This modifier can be cast off by a copy, so it's not generally what you want here. Switch to const T * instead.

lib/FrontendTool/LoadedModuleTrace.cpp

@@ -699,7 +699,7 @@ bool swift::emitLoadedModuleTraceIfNeeded(ModuleDecl *mainModule,
   assert(!ctxt.hadError() &&
          "We should've already exited earlier if there was an error.");
 
-  StringRef loadedModuleTracePath = input.loadedModuleTracePath();
+  auto loadedModuleTracePath = input.loadedModuleTracePath();
   if (loadedModuleTracePath.empty())
     return false;
   std::error_code EC;