Use Windows localtime_s() if available

If available, use localtime_s() instead of localtime().

As localtime_s() is part of the Windows API, the compile
check with localtime_s() should only work for those systems.

Note we are not using AC_CANONICAL_HOST and then checking the
$host_os here. Either localtime_s() is available, then we
can use it. Or localtime_s() is not available, then we cannot
use it.

All of that is independent of what exactly the $host_os value
actually is, and whether we have listed all appropriate values
in the list of matches.

Closes: #57
Closes: #66

configure.ac

@@ -208,8 +208,22 @@ GP_GETTEXT_FLAGS()
 dnl ---------------------------------------------------------------------------
 dnl Thread-safe functions
 dnl ---------------------------------------------------------------------------
+AC_MSG_CHECKING([for localtime_s])
+AC_LINK_IFELSE([AC_LANG_PROGRAM([[
+  #include <time.h>
+]], [[
+  localtime_s(NULL, NULL);
+]])], [dnl
+  have_localtime_s="yes"
+  AC_DEFINE([HAVE_LOCALTIME_S], [1], [Define to 1 if you have localtime_s()])
+], [dnl
+  have_localtime_s="no"
+])
+AC_MSG_RESULT([$have_localtime_s])
+
 AC_CHECK_FUNCS([localtime_r])
 
+
 dnl ---------------------------------------------------------------------------
 dnl Compiler/Linker Options and Warnings
 dnl ---------------------------------------------------------------------------

libexif/exif-entry.c

@@ -1641,14 +1641,17 @@ exif_entry_initialize (ExifEntry *e, ExifTag tag)
 	case EXIF_TAG_DATE_TIME_DIGITIZED:
 	{
 		time_t t;
-#ifdef HAVE_LOCALTIME_R
+#if defined(HAVE_LOCALTIME_R) || defined(HAVE_LOCALTIME_S)
 		struct tm tms;
 #endif
 		struct tm *tm;
 
 		t = time (NULL);
 #ifdef HAVE_LOCALTIME_R
 		tm = localtime_r (&t, &tms);
+#elif HAVE_LOCALTIME_S
+		localtime_s (&tms, &t);
+		tm = &tms;
 #else
 		tm = localtime (&t);
 #endif