mktime: call tzset as per POSIX Problem reported by Ludovic Courtès in: http://lists.gnu.org/archive/html/bug-gnulib/2016-06/msg00068.html * lib/mktime.c (mktime) [!_LIBC && HAVE_TZSET]: Call tzset. * m4/mktime.m4 (gl_FUNC_MKTIME): Check for tzset.