ssl: Fix memcmp() IPv6 address size

clang spotted the misplaced parentheses:

    ssl.c:120:72: warning: size argument in 'memcmp' call is a comparison
          [-Wmemsize-comparison]
      ...!memcmp(&a6->sin6_addr, &b6->sin6_addr, sizeof(a6->sin6_addr) &&
                                                 ~~~~~~~~~~~~~~~~~~~~~~^~

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
buildsys: Disable -Wformat-nonliteral

The new charset translation functions need to use caller-supplied format
strings:

      CC       openconnect-main.o
    main.c:422:22: warning: format string is not a string literal
          [-Wformat-nonliteral]
                    return vfprintf(f, fmt, args);
                                       ^~~
    main.c:424:29: warning: format string is not a string literal
          [-Wformat-nonliteral]
            ret = vasprintf(&utf8_str, fmt, args);
                                       ^~~

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>