lib-test-string_helpersc-add-string_get_size-tests-v5

lib-test-string_helpersc-add-string_get_size-tests-v5

- Single quotes in pr_warn() to see empty strings [Andy Shevchenko].
- Check for test validity compile-time [Rasmus Villemoes, Andy Shevchenko].
- All __test_string_get_size() arguments are const.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: James Bottomley <JBottomley@Odin.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>