curl.h: include <sys/select.h> on SerenityOS

Closes #10006

include/curl/curl.h

@@ -92,7 +92,7 @@
     defined(__CYGWIN__) || defined(AMIGA) || defined(__NuttX__) || \
    (defined(__FreeBSD_version) && (__FreeBSD_version < 800000)) || \
    (defined(__MidnightBSD_version) && (__MidnightBSD_version < 100000)) || \
-    defined(__sun__)
+    defined(__sun__) || defined(__serenity__)
 #include <sys/select.h>
 #endif