--- src/config.in~

+++ src/config.in

@@ -1138,6 +1138,8 @@ SYSTEM_PURESIZE_EXTRA seems like the lea

 #ifdef HAVE_ALLOCA_H

 # include <alloca.h>

+#elif __FreeBSD__

+# include <stdlib.h>

 #elif defined __GNUC__

 # define alloca __builtin_alloca

 #elif defined _AIX