Use _Exit(0) on win32, always use _Exit(1) in log_error()

kernel/driver.cc

@@ -509,6 +509,11 @@ int main(int argc, char **argv)
 		free(hist_list);
 #endif
 
+	log_flush();
+#ifdef _WIN32
+	_Exit(0);
+#endif
+
 	yosys_shutdown();
 
 	return 0;

kernel/log.cc

@@ -208,7 +208,7 @@ void logv_error(const char *format, va_list ap)
 	log_files = backup_log_files;
 	throw 0;
 #else
-	exit(1);
+	_Exit(1);
 #endif
 }