[LTP] [PATCH] Enable including config.mk and features.mk for *clean targets

[Yuriy K. <yur...@sy...>]

It's necessary for correct cleaning. E.g. open_posix_testsuite
is not cleaned without including these .mk files. However it's
not an error if these files does not exist while cleaning.

Signed-off-by: Yuriy Kolerov <yur...@sy...>
---
 include/mk/env_pre.mk | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)