Unimplemented strftime format %U #1429
Description
The glib test date calls strftime with %U as one of the modifiers. The man page states:
%U The week number of the current year as a decimal number, range 00 to 53, starting with the first Sunday as the first day of week 01. See also %V and %W. (Calculated from tm_yday and tm_wday.).
We should implement this to improve compliance with the testsuite.