test: unit tests for strstr() and strnstr()

Add unit tests for the library functions.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
[jf: drop unwanted change to lib/string.c]
Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
1 file changed