string: Allow use of test-string.h for non-ifunc implementations.

Mark two variables as unused to silence warning when using
test-string.h for non-ifunc implementations.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

string/test-string.h

@@ -130,8 +130,8 @@ cmdline_process_function (int c)
 /* Increase size of FUNC_LIST if assert is triggered at run-time.  */
 static struct libc_ifunc_impl func_list[32];
 static int func_count;
-static int impl_count = -1;
-static impl_t *impl_array;
+static int impl_count __attribute__ ((unused)) = -1;
+static impl_t *impl_array __attribute__ ((unused));
 
 # define FOR_EACH_IMPL(impl, notall) \
   impl_t *impl;								\