python/build: add support for fallback download URLs

python/build/makeproject.py

@@ -1,11 +1,11 @@
 import subprocess, multiprocessing
-from typing import Optional
+from typing import Optional, Sequence, Union
 
 from build.project import Project
 from .toolchain import AnyToolchain
 
 class MakeProject(Project):
-    def __init__(self, url: str, md5: str, installed: str,
+    def __init__(self, url: Union[str, Sequence[str]], md5: str, installed: str,
                  install_target: str='install',
                  **kwargs):
         Project.__init__(self, url, md5, installed, **kwargs)