commit fcf1b6a3

 upstream.

added to kbuild documentation. Provides more official info on building
kernels with Clang and LLVM than our wiki.

Suggested-by: Kees Cook <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Reviewed-by: Sedat Dilek <[email protected]>
Signed-off-by: Nick Desaulniers <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>