Add <poll.h> detection as well

configure.in

@@ -884,6 +884,7 @@ dnl AC_SYS_RESTARTABLE_SYSCALLS
 
 dnl ----------------------------------------------------------------
 AC_CHECK_FUNCS( poll )
+AC_CHECK_HEADERS( poll.h )
 
 dnl ----------------------------------------------------------------
 # strerror checks

include/portable.h.in

@@ -482,6 +482,9 @@
 /* Define if you have the <openssl/ssl.h> header file.  */
 #undef HAVE_OPENSSL_SSL_H
 
+/* Define if you have the <poll.h> header file.  */
+#undef HAVE_POLL_H
+
 /* Define if you have the <process.h> header file.  */
 #undef HAVE_PROCESS_H