Details on this package are located in Section 6.9.2, “Contents of Linux API Headers.”
The Linux API Headers (in linux-4.0.3.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, placing them in the standard package staging directory:
make INSTALL_HDR_PATH=debian/tmp/tools headers_install
Create the package archive:
buildpkg --package=linux-headers-pass1
Install the package:
dpkg -i ../linux-headers-pass1_4.0.3_*.deb
Details on this package are located in Section 6.9.2, “Contents of Linux API Headers.”