Kernel headers
Most "normal" programs don't need kernel headers and in fact may break if you use them directly; instead they should be compiled against the headers with which glibc was built, which are the versions in /usr/include/linux and /usr/include/asm
of the Debian system.
So do not put symlinks to the directories in /usr/src/linux from /usr/include/linux and /usr/include/asm, as suggested by some outdated documents.
If you need particular kernel headers for some kernel-specific application programs, alter the makefile(s) so that their include path points to dir-of-particular-kernel-headers/include/linux and dir-of-particular-kernel-headers/include/asm.