Gcc 8 has strict (and sometimes buggy) tests for strncpy() misuse.

A common pattern in the JDK is:

    const size_t not_impl_len = strlen(not_impl);
    *str = NEW_C_HEAP_ARRAY(char, not_impl_len+1, mtTracing);
    strncpy(*str, not_impl, not_impl_len);
    (*str)[not_impl_len] = '\0';

More efficient code that does not cause GCC warnings would use strncpy()
to add the trailing null, resulting in shorter code:

     strncpy(*str, not_impl, not_impl_len);
    (*str)[not_impl_len] = '\0';

becomes:

    strncpy(*str, not_impl, not_impl_len+1);

(found by compiling with GCC 8.1)