Details on this package are located in Section 6.7.2, “Contents of Linux API Headers.”
The Linux API Headers (in linux-5.5.3.tar.xz) expose the kernel's API for use by Glibc.
The Linux kernel needs to expose an Application Programming Interface (API) for the system's C library (Glibc in LFS) to use. This is done by way of sanitizing various C header files that are shipped in the Linux kernel source tarball.
Make sure there are no stale files embedded in the package:
make mrproper
Now extract the user-visible kernel headers from the source. The
recommended make target “headers_install” cannot be used,
because it requires rsync, which
may not be available. The headers are first placed in ./usr, then copied to the needed location.
make headers cp -rv usr/include/* /tools/include
Details on this package are located in Section 6.7.2, “Contents of Linux API Headers.”