If the kernel headers aren't installed we can't build all the tests.
Add a new make target rule 'khdr' in the file lib.mk to generate the
kernel headers and that gets include for every test-dir Makefile that
includes lib.mk If the testdir in turn have its own sub-dirs the
top_srcdir needs to be set to the linux-rootdir to be able to generate
the kernel headers.
Signed-off-by: Anders Roxell <email@example.com>
Reviewed-by: Fathi Boudra <firstname.lastname@example.org>
Signed-off-by: Shuah Khan (Samsung OSG) <email@example.com>