Xcode: Create separate rerun dependencies for subprojects (#12616)

Generate the rerun dependency file for the top-level project() and each
subdirectory project() into the corresponding build directory.  Do not
clobber them all with the one for the last subproject.  This mistake was
left from when the Xcode generator did not produce subprojects.

Source/cmGlobalXCodeGenerator.cxx

@@ -458,8 +458,7 @@ void cmGlobalXCodeGenerator::CreateReRunCMakeFile(
   std::vector<std::string>::iterator new_end =
     std::unique(lfiles.begin(), lfiles.end());
   lfiles.erase(new_end, lfiles.end());
-  std::string dir = mf->GetHomeOutputDirectory();
-  this->CurrentReRunCMakeMakefile = dir;
+  this->CurrentReRunCMakeMakefile = mf->GetStartOutputDirectory();
   this->CurrentReRunCMakeMakefile += "/CMakeScripts";
   cmSystemTools::MakeDirectory(this->CurrentReRunCMakeMakefile.c_str());
   this->CurrentReRunCMakeMakefile += "/ReRunCMake.make";