klibc: klcc: consider --sysroot option and override gcc-cross encoded sysroot

For the recipes built with klcc-cross it is necessary to
pass --sysroot otherwise we default to the one encoded in gcc-cross which
actually is the 'first one' built.
The issue was revealed when building for armv4 after having built for armv5te:
the produced binaries did contain Illegal Instruction (bx lr).

Use ${TOOLCHAIN_OPTIONS} variable to specify --sysroot=${STAGING_DIR_TARGET}

Signed-off-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>