搭建源码镜像

[fwerkor]

Describe the feature

即编译时会自动下载到/dl的部分，可以在projectsmirrors配置。
从openwrt的源拉的话太慢了

Additional info

No response

[github-actions]

This GitHub issue suggests adding support for configuring a custom source mirror in the projectsmirrors configuration for dependencies that are automatically downloaded into the /dl directory during compilation. The user highlights that downloading from the default OpenWrt source is too slow and implies that the feature would improve download speeds during the build process. No additional information or responses are provided.

[fwerkor]

等哪次用了buildbot再说吧，那样更全一点，直接丢到repo上去就行