python3: disable usage of wcsftime (broken in uClibc)

python3: disable usage of wcsftime (broken in uClibc)

Python 3 prefers usage of wcsftime() over strftime() if it's available,
however this function returns just an empty string in some older
uClibc versions. Proposed solution disables detection of wcsftime() in
./configure that results in HAVE_WCSFTIME being undefined, effectively
disabling branches of code that use possibly broken wcsftime().

See: http://lists.busybox.net/pipermail/uclibc/2014-November/048718.html

Signed-off-by: Jan Čermák <redacted>