Detect and use sys/select.h required by POSIX for select

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@40530 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

configure.in

@@ -1801,6 +1801,11 @@ case "${host}" in
   ;;
 esac
 
+dnl POSIX needs this for select(), but old systems don't have it
+if test "$USE_UNIX" = 1 ; then
+    AC_CHECK_HEADERS([sys/select.h])
+fi
+
 dnl ---------------------------------------------------------------------------
 dnl Checks for compiler characteristics
 dnl ---------------------------------------------------------------------------