Merge branch 'kbuild/resolve_btfids: Invoke resolve_btfids'

Jiri Olsa says:

====================

hi,
resolve_btfids tool is used during the kernel build,
so we should clean it on kernel's make clean.

v2 changes:
  - add Song's acks on patches 1 and 4 (others changed) [Song]
  - add missing / [Andrii]
  - change srctree variable initialization [Andrii]
  - shifted ifdef for clean target [Andrii]

thanks,
jirka
====================

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>