Configure: add missing check for used funcs

Configure: add missing check for used funcs

Based on autoscan report:
configure.ac: warning: missing AC_CHECK_FUNCS([ftruncate]) wanted by: formats/ctf/writer/writer.c:237
configure.ac: warning: missing AC_CHECK_FUNCS([gethostbyname]) wanted by: formats/lttng-live/lttng-live-comm.c:122
configure.ac: warning: missing AC_CHECK_FUNCS([localtime_r]) wanted by: formats/ctf/ctf.c:341
configure.ac: warning: missing AC_CHECK_FUNCS([memset]) wanted by: converter/babeltrace-log.c:228
configure.ac: warning: missing AC_CHECK_FUNCS([mkdir]) wanted by: converter/babeltrace-log.c:404
configure.ac: warning: missing AC_CHECK_FUNCS([rmdir]) wanted by: converter/babeltrace-log.c:467
configure.ac: warning: missing AC_CHECK_FUNCS([setenv]) wanted by: include/babeltrace/compat/utc.h:71
configure.ac: warning: missing AC_CHECK_FUNCS([socket]) wanted by: formats/lttng-live/lttng-live-comm.c:129
configure.ac: warning: missing AC_CHECK_FUNCS([strchr]) wanted by: converter/babeltrace-log.c:244
configure.ac: warning: missing AC_CHECK_FUNCS([strdup]) wanted by: converter/babeltrace.c:701
configure.ac: warning: missing AC_CHECK_FUNCS([strerror]) wanted by: formats/ctf/ctf.c:682
configure.ac: warning: missing AC_CHECK_FUNCS([strndup]) wanted by: formats/lttng-live/lttng-live-comm.c:280
configure.ac: warning: missing AC_CHECK_FUNCS([strrchr]) wanted by: converter/babeltrace-log.c:334
configure.ac: warning: missing AC_CHECK_FUNCS([strtoull]) wanted by: converter/babeltrace.c:354
configure.ac: warning: missing AC_CHECK_FUNCS([tzset]) wanted by: include/babeltrace/compat/utc.h:72

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>