tests/date.c: include config.h to expose Vista+ macros
tests/date.c: include config.h to expose Vista+ macros

date.c uses SUBLANG_LITHUANIAN_LITHUANIA which is Vista+
Include config.h so that _WIN32_WINNT is defined and the newer macros
are exposed.

This fixes the build under MinGW.

https://bugzilla.gnome.org/show_bug.cgi?id=793729

endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib,endlessm/glib