port: Add alternative for isinf.
diff --git a/configure.ac b/configure.ac
index 5c02fb4..e38f5e7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1607,6 +1607,14 @@
AC_DEFINE(HAVE_DAYLIGHT, 1, [Define if you have the daylight variable])
fi
+dnl Check for isinf
+AC_CACHE_CHECK([for isinf], ac_cv_have_isinf,
+ AC_LINK_IFELSE([AC_LANG_PROGRAM([[#include <math.h>]], [[float f = 0.0; isinf(f)]])],[ac_cv_have_isinf="yes"],[ac_cv_have_isinf="no"]))
+if test "$ac_cv_have_isinf" = "yes"
+then
+ AC_DEFINE(HAVE_ISINF, 1, [Define to 1 if you have the `isinf' function.])
+fi
+
dnl *** check for the need to define platform-specific symbols
case $host_cpu in
