Most build products aren't "before build-script-impl"

Author: DougGregor

utils/swift_build_support/swift_build_support/products/product.py

@@ -61,6 +61,14 @@ def is_build_script_impl_product(cls):
         """
         raise NotImplementedError
 
+    @classmethod
+    def is_before_build_script_impl_product(cls):
+        """is_before_build_script_impl_product -> bool
+
+        Whether this product is build before any build-script-impl products.
+        """
+        return False
+
     @classmethod
     def is_ignore_install_all_product(cls):
         """is_ignore_install_all_product -> bool