cmDyndepCollation: add a query for whether an object is BMI-only

The collator needs to know that the object *is* a BMI so that it can
just use the location directly.

Source/cmDyndepCollation.cxx

@@ -666,3 +666,16 @@ bool cmDyndepCollation::IsObjectPrivate(
   auto const& file_set = fileset_info_itr->second;
   return !cmFileSetVisibilityIsForInterface(file_set.Visibility);
 }
+
+bool cmDyndepCollation::IsBmiOnly(cmCxxModuleExportInfo const& exportInfo,
+                                  std::string const& object)
+{
+#ifdef _WIN32
+  auto object_path = object;
+  cmSystemTools::ConvertToUnixSlashes(object_path);
+#else
+  auto const& object_path = object;
+#endif
+  auto fs = exportInfo.ObjectToFileSet.find(object_path);
+  return (fs != exportInfo.ObjectToFileSet.end()) && fs->second.BmiOnly;
+}

Source/cmDyndepCollation.h

@@ -53,4 +53,7 @@ struct cmDyndepCollation
                                   cmDyndepMetadataCallbacks const& cb);
   static bool IsObjectPrivate(std::string const& object,
                               cmCxxModuleExportInfo const& export_info);
+
+  static bool IsBmiOnly(cmCxxModuleExportInfo const& exportInfo,
+                        std::string const& object);
 };