tests: kernel: errno: Add Newlib test config.

Added because previously, Zephyr used API incompatible with Newlib
for errno handling. Even with Newlib compatibility changes, we
override the function which is defined in Zephyr SDK libc.a, so
makes sense to ensure thsi works as expected.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>