Fixes [YOCTO #9988]
Added a link to the MULTIMACH_HOST_SYS variable from the
STAGING_DIR_HOST variable where it is referenced.
(From yocto-docs rev: 0f72b58a7bc1271245d139726f1145d5d99acee4)
Signed-off-by: Scott Rifenbark <srifenbark@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>