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
in the subdir 'package/' and run 'make' from this directory.