Add helper to log Windows system errors

It will help to log errors returned by GetLastError() or
WSAGetLastError():
 - <https://docs.microsoft.com/en-us/windows/win32/api/errhandlingapi/nf-errhandlingapi-getlasterror>
 - <https://docs.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-wsagetlasterror>
 - <https://docs.microsoft.com/en-us/windows/win32/debug/system-error-codes#system-error-codes>

Always log the errors in English to be able to read them in bug reports.

app/src/util/log.h

@@ -26,4 +26,10 @@ sc_set_log_level(enum sc_log_level level);
 enum sc_log_level
 sc_get_log_level(void);
 
+#ifdef _WIN32
+// Log system error (typically returned by GetLastError() or similar)
+bool
+sc_log_windows_error(const char *prefix, int error);
+#endif
+
 #endif