libowfat target-build fails on macos due to using system `ar` and
`ranlib` tools not compatible with the objects generated by
OpenWrt GCC toolchain.
This patch specifies CROSS= make flag that is used as a prefix for
`ar` and `ranlib` tools.
This patch also specifies CCC= make flag due to CCC= has invalid
value after specifying CROSS= make flag (CCC=$(CROSS)$(CC))
Signed-off-by: Sergey V. Lobanov <sergey@lobanov.in>