dnl Substitute OCaml flags and packages.
AC_SUBST([OCAMLFLAGS], ["-g -safe-string -warn-error CDEFLMPSUVYZX+52-3"])
-AC_SUBST([OCAMLPACKAGES], ["-package str,unix"])
+AC_SUBST([OCAMLPACKAGES], ["-package str,unix,threads -thread"])
dnl Produce output files.
AC_CONFIG_HEADERS([config.h])