selftests: add headers_install to lib.mk

2018-09-05T14:12:09Z

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 Reviewed-by: Fathi Boudra Signed-off-by: Shuah Khan (Samsung OSG)

kernel/scripts/subarch.include, branch linux-5.7.y

selftests: add headers_install to lib.mk