curl.h: <sys/select.h> for OpenBSD

curl.h should also include <sys/select.h> on OpenBSD to reliably
pull in select().  Typically, including <sys/time.h> will be enough,
but not if strict standards-compliance is requested (e.g. by defining
_XOPEN_SOURCE).
diff --git a/include/curl/curl.h b/include/curl/curl.h
index 5c63dd8..9bee934 100644
--- a/include/curl/curl.h
+++ b/include/curl/curl.h
@@ -69,7 +69,7 @@
    require it! */
 #if defined(_AIX) || defined(__NOVELL_LIBC__) || defined(__NetBSD__) || \
     defined(__minix) || defined(__SYMBIAN32__) || defined(__INTEGRITY) || \
-    defined(ANDROID) || defined(__ANDROID__) || \
+    defined(ANDROID) || defined(__ANDROID__) || defined(__OpenBSD__) || \
    (defined(__FreeBSD_version) && (__FreeBSD_version < 800000))
 #include <sys/select.h>
 #endif