immortalwrt-mt798x/target/sdk/files

This is the OpenWrt SDK. It contains a stripped-down version of
the buildroot. You can use it to test/develop packages without
having to compile your own toolchain or any of the libraries
included with OpenWrt.

To use it, just put your buildroot-compatible package directory
(including its dependencies) in the subdir 'package/' and run
'make' from this directory.

To make dependency handling easier, you can use ./scripts/feeds
to install any core package that you need