acording to this linux man page : https://linux.die.net/man/3/localtime_r one should include at least _POSIX_C_SOURCE
afaics, localtime_r is used only in elementary (git grep shows it is in tests, examples, lib and a module) and they include Elementary.h and Efl_UI.h
but what is interesting is that mingw-w64 also declares localtime_r if _POSIX_C_SOURCE is defined (i guess that they use localtimee_s which is declared since Vista. localtime_r and localtime_s have arguments in the reverse order). Currently, i define localtime_r in Evil using localtime_s. So that would reduce even more the size of Evil(ness) if we define _POSIX_C_SOURCE just before including time.h in Elementary.h and Efl_UI.h.
so do you think that there is a problem if we define _POSIX_C_SOURCE just before including time.h in Elementary.h and Efl_UI.h ?