Bugfix
   * Set _POSIX_C_SOURCE to at least 200112L in C99 code. Reported in #3420 and fix submitted in #3421 by Nia Alarie.

Add ChangeLog.d entry for PR3421
Add ChangeLog.d entry for PR3421

Signed-off-by: nia <5ad140d5f4b7cad9d45ac9c0d051724ab2960e88@netbsd.org>
