Look for fmtcheck(3) function.

git-svn-id: http://www.varnish-cache.org/svn/trunk/varnish-cache@1881 d4fa192b-c00b-0410-8231-f00ffab90ce4

configure.ac

@@ -84,6 +84,7 @@ AC_FUNC_STRERROR_R
 AC_CHECK_FUNCS([socket])
 AC_CHECK_FUNCS([strptime])
 AC_CHECK_FUNCS([sendfile])
+AC_CHECK_FUNCS([fmtcheck])
 
 # These functions are provided by libcompat on platforms where they
 # are not available