w32: Add implementation of gmtime_r, localtime_r

Those functions are missing in MinGW.

Some versions of MinGW-w64 include defines for gmtime_r and localtime_r.
Older versions of these macros are buggy (they return a pointer to a
static variable), therefore we don't want them. Newer versions are
similar to the code used here, but without the memset.

The implementation which is used here is not strictly reentrant,
but sufficiently good for QEMU on w32 or w64.
Signed-off-by: NStefan Weil <sw@weilnetz.de>
[blauwirbel@gmail.com: added comment about locking]
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

oslib-win32.c

@@ -74,6 +74,30 @@ void qemu_vfree(void *ptr)
     VirtualFree(ptr, 0, MEM_RELEASE);
 }
 
+/* FIXME: add proper locking */
+struct tm *gmtime_r(const time_t *timep, struct tm *result)
+{
+    struct tm *p = gmtime(timep);
+    memset(result, 0, sizeof(*result));
+    if (p) {
+        *result = *p;
+        p = result;
+    }
+    return p;
+}
+
+/* FIXME: add proper locking */
+struct tm *localtime_r(const time_t *timep, struct tm *result)
+{
+    struct tm *p = localtime(timep);
+    memset(result, 0, sizeof(*result));
+    if (p) {
+        *result = *p;
+        p = result;
+    }
+    return p;
+}
+
 void socket_set_block(int fd)
 {
     unsigned long opt = 0;

qemu-os-win32.h

@@ -68,6 +68,12 @@
 /* Declaration of ffs() is missing in MinGW's strings.h. */
 int ffs(int i);
 
+/* Missing POSIX functions. Don't use MinGW-w64 macros. */
+#undef gmtime_r
+struct tm *gmtime_r(const time_t *timep, struct tm *result);
+#undef localtime_r
+struct tm *localtime_r(const time_t *timep, struct tm *result);
+
 static inline void os_setup_signal_handling(void) {}
 static inline void os_daemonize(void) {}
 static inline void os_setup_post(void) {}