Let our own timegm() for Windows behave the same (buggy) way as the POSIX version of timegm()....

src/platform_windows.cpp

@@ -410,7 +410,7 @@ DYNAMIC_API time_t timegm(timestamp *timeptr)
     if (result == -1)
         return -1;
 
-    return (result - timeptr->tm_gmtoff);
+    return result;
 }
 
 void uuid_generate_random(pEpUUID out)

src/platform_windows.h

@@ -54,6 +54,8 @@ int dlclose(void *handle);
 void *dlsym(void *handle, const char *symbol);
 int mkstemp(char *templ);
 
+// Nota bene: It does _not_ respect timeptr->tm_gmtoff, so it behaves the same as its POSIX original.
+//            Use timegm_with_gmtoff() from <pEp/timestamp.h> or that.
 DYNAMIC_API time_t timegm(timestamp *timeptr);
 
 #ifndef strdup