Compile IPA modules with C11 extensions
    
    - define __STDC_WANT_LIB_EXT1__ to get C11 extensions like memset_s() for
      Samba's ZERO_STRUCT() macro, see
      https://en.cppreference.com/w/c/string/byte/memset
    - _DEFAULT_SOURCE enables features like htole16() from endian.h, see
      http://man7.org/linux/man-pages/man3/endian.3.html
    - _POSIX_C_SOURCE >= 200809 enables features like strndup() from string.h,
      see http://man7.org/linux/man-pages/man3/strndup.3.html
    - time_t is no longer implicitly defined, include time.h
    - typeof() is only available as GNU extension. Use explicit types
      instead of generic __typeof__().
    
    Fixes: https://pagure.io/freeipa/issue/7858
    Signed-off-by: Christian Heimes <cheimes@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>